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Don't you think it's time for engineers all over the world to use the same system?? Ofcourse this must be the metric system!



In many cases, I believe the system should be governed by what the suppliers have available and what the "mechanics" are used to.  In the US, there are a lot of things such as bolts, rods, beams etc. that are still manufactured in English units.  Admittedly, the US school system has done a dismal job of teaching metrics - my opinions here are no surprise.  I think it is the duty of the Engineers to take the element of human failure/mistake out of the design to the maximum extent practical.  Why should decide that a 1/4-20, grade 5 bolt will substitute for a 5 mm 8.8 bolt, the degreed engineer, the purchasing agent or the guy assembling the component?  I have happily worked in several systems, according to the majority around me at the time to avoid confusion. Look at pressure for one example; inches of mercury, centimeters of mercury, inches of water, feet of water, bars, pascals, atmospheres, pounds per square inch - depends on the component and country you're dealing with.



It would be nice, but until the U.S. makes the switch to metric for get it.
  I’m sure also that many of us are growing accustom to the imperial system (like I have) because the majority of companies customer bases are in the states.


Depending on the industry, in some cases the US already is metric.  Nearly all engineering for American automobiles is done in metric units.  This has been the case for a decade.  There are still vestiges of the English system (generally found in the test laboratories and plants, which are older and consist of older-generation workers).  However, parts are designed, analyzed, and spec'ed in metric.
Everyone other than engineers and scientists are still kicking and screaming . . .


Why do European countries who try to badger the USA into metrification not fully follow their own advice.  In the process industry, pressure is often referred to in km/cm^2, not in Pa, kPa, MPa, or bar?  This is only one example of many I have run across.


The metric rules seem to be lengths given in millimeters, area loads in kPa and volume in liters.

Wheee. I think we've all been using kilo-pounds for a long time, why change?

Now, I will gladly switch to metric when:

a) kilometer is pronounced correctly. It's a KILL-O-METER not a kilom-eter.

b) Length mesurement changes to Angstroms.

d) Volume is stricly given in deciliters.


I'll switch to metric when they finally get a decent thread pitch and tolerance for each thread size.  Fine threads are too fine and course threads are too course.

And I still don't get the genious behind the tolerancing scheme.  I put H7 on a drawing and the tolerance is different depending on the nominal hole size.  What a PITA to remember.  And why do I have to clarify between h7 and H7?  Is capitalization that important on a drawing?  What happened to being able to print everything in all caps for clarity.  I'm surprised ISO/Metric drawing standards haven't allowed for cursive writing on the drawing face yet.  SHEESH!

<end of rant... thanks for listening>



Personally, I prefer to perform calculations using the SI system.  While the system uses metric units, there is a standard metric unit for everything, and every standard unit reduces to kilograms, meters, and seconds.  I try not to use prefixes on anything while doing calculations (ironicly, there is already a prefix on the kilogram standard, which always bothered me).  There is less confusion that way, and I tend to make fewer mistakes.  The main problem is that this system yields unwieldy numbers.  So, in the end, I tend to convert the "answer" into "convenient" units.  Usually, convenient is defined as a unit that allows for a "pretty" number.

For example, can you imagine an American bragging that their new Corvette had 260,995 Watts of power, instead of 350 horsepower?  Or how about an American who bought a house on a 20,234 square meter lot, instead of a five acre lot?  It's just not gonna happen!  Each industry has units associated with it that usually allow the engineers to work with "nice" numbers, regardless of whether English or metric units comprise those units.  Furthermore, those industries have used those units for so long that they have been ingrained into the culture.  People begin to "get a feel" for those units.  The major difference is that with metric units, there is a tendency towards using prefixes to tame numbers by factors of ten.  In the English system, we show an utter disregard for the decimal system, invent a completely new unit, and usually try to give it a funny name.

America has already tried to switch to metric units.  Simply put: it didn't take.  Of course, at the time, people feared that switching to metric units was the first step towards switching to communism.  Maybe now that the Cold War is over, we should give it another shot?  My sneaking suspicion is that it still won't take.



Things could be worse.

Try living and working in Canada where we are caught in a eternal state of limbo between SI and Imperial. I listen to the morning news to find out the temperature in celsius while drinking a cup of coffee. Then I drive 15 kilometres to work at 30 miles per hour where I perform calculations on 7-1/16" 35 MPa flange connections. On the way home I pick up a litre of milk and a pound of butter. I think you get the picture.


The world is metric. It’s just the US (and Yemen) that is not.

Because of our proximity to the US here in Canada we tend to use a hybrid system. Until our largest trading partner joins the remainder of the world in adopting the most rational system of measurement, we will continue to have vestiges of the imperial system.

To reject the metric system because no one wants to say that they bought a 20,234 sq m lot demonstrates that you simply do not understand measurement systems. Is the 5-acre lot exactly 5 acres to 5 significant digits? (5.0000) I think not. Why not buy a 2-hectare lot instead?  

There are “nice” numbers in the metric system. My old Mopar 440 is now a 7.2-liter engine. Your Corvette puts out 261 kW. To have to remember a few prefixes (many of which we already use. How many Megs of RAM do you have in your computer, How many Gigahertz is the processor? How many kilobytes is that document file?) is a lot simpler than remembering that an acre has 43,560 sq ft or that there are 160 oz in a gallon (imperial not US gallon which is only 128 oz.) or that 60 MPH is 88 FPS. or any of a hundred different conversion factors necessary to work in the imperial system.

Yes, switching to the metric system is difficult. There are ingrained cultural reasons that make the conversion harder. Canada has been using Celsius for 28 years now and there are still some radio stations that give temperatures in Fahrenheit. We should have simply converted totally and not allowed soft conversions why not buy 500 g of butter instead of 454 g.  Why are fluorescent light tubes 1 220 mm long? Why not 1 200 mm?

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion


In this age of calculators, spreadsheets, programming, etc, in one sense it really shouldn't matter what system we use.  Conversion utilities abound.  And precision is simply a matter of what your needed tolerances are.  Cabinetmakers work to 64ths of an inch, while machinists work to thousandths (or their metric equivalents).  But:  Hush is right on when he refers to our fractured lives here in Canada.  I'm old enough to think and feel in Imperial, but must work professionally in metric.  I still don't have any intuitive feel for a length of, say, 1500 mm (without first mentally translating to metres, and then on to yards each time), whereas the inch (still called "un pouce" - "a thumb" - in French), or the foot, are human-derived measures with which I am most connected.  I can "feel" how much a pound weighs, but have trouble with much direct insight into kilonewtons.  And then, of course:  the concatenation of units with which we often deal (try deriving the fundamental units for specific enthalpy, or for dynamic viscosity) are complex enough, without worrying about conversions.  Thank the exponents-that-be for computers!

RDK is right when he says that switching to metric is difficult.  And I agree also that if we are going to switch, let's do it completely and never look back.  It WOULD be far better to live and work in only one system - whatever it is!  But this is not our reality here in the limbo of water that boils at two different integers.  

The real trouble for us engineers, I think, springs from the danger of translation between the two systems, and the increased chance for error at that juncture.  I do not know how others handle this situation, but I design structural systems in metric (because all our LSD-based codes are in metric), and at the very end where necessary, I convert to Imperial so that contractors and suppliers can understand what it is I am talking about.  

As an aside: the study of units (and their historical beginnings) from a sociological perspective is fascinating in itself.  Taking a purely intuitive approach, who of our not-so-distant ancestors would have ever dreamed that the fundamental units ("fundamental" in metric, that is) of mass, length, and time (two times, no less!), when combined in a certain way, would produce the unit of force?  This is strange magic indeed.

Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.


Well this certainly turned into an interesting discussion!  Let me clear up some things.

As I mentioned, I prefer the metric system.  I'm a recent grad, and most of the classes I took, both as an undergraduate and graduate student, exclusively used the metric system.  Now that I'm working, however, I am almost forced into using the English system.  Believe me, many of the engineers and scientists in the US would love to switch to the metric system (especially the younger ones), but, as RDK pointed out, it's tough to switch.

I must take exception with one of RDK's comments.  Americans understand measurement systems just fine.  In fact, one reason we can't seem to be able to kick the English system is because we have been trying to use measurement systems that are understandable.  As Aton pointed out, the inch and the foot are human-derived measurements.  Everyone has seen movies with carriages drawn by horses.  We have a feel for the power of one horse, or six horses for a stage-coach.  To this day, when I think of a Vette with 350 horse power, I think of 350 horses pulling that car!  Unfortunately, the price we pay for using human-derived measurements is ugly conversion factors.  Guess you can't have your cake and eat it too.

Engineers and scientists get used to using units they have no "feel" for.  As Aton pointed out, almost no one has a feel for enthalpy or viscosity.  Or how about entropy or thermal conductivity?  Who has a feel for nanometers or picofarrads?  Since engineers get used to working with these units, many have no qualms with switching to metric.  As for the rest of the country, good luck!

Now for a little story.  Not too long ago an unmanned NASA shuttle went off-course and was eventually lost in deep space.  NASA engineers struggled to find the source of the problem, and recalculated their formulas and equations.  It ended up that one systems group was using metric units and the other English.  They had forgotten to convert into one language.  And these guys were rocket scientists!

The unfortunate reality is that there will always be different measuring systems.  Despite this, we can hopefully speak the same language in the end.



Here is a little light hearted story that explains many things.

The US standard railroad gauge (width between the two rails) is 4 feet, 8.5 inches. That's an exceedingly odd number. Why was that gauge used? Because that's the way they built them in England, and the US railroads were
Built by English expatriates. Why did the English build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used. Why did "they" use that gauge then?  Because the people who built the tramways used
the same jigs and tools that they used for building wagons which used that wheel spacing.

Okay! Why did the wagons have that particular odd wheel spacing? Well, If they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts. So who built those old rutted roads?

The first long distance roads in Europe and England were built by Imperial Rome for their legions. The roads have been used ever since. And the ruts in the roads?

Roman war chariots first formed the initial ruts, which everyone else had to match for fear of destroying their wagon wheels. Since the chariots were made for (or by) Imperial Rome, they were all alike in the matter of wheel

The United States standard railroad gauge of 4 feet, 8.5 inches derives the original specification for an Imperial Roman war chariot. Specifications and bureaucracies live forever!

So the next time you are handed a specification and wonder what horse's Ass came up with it, you might be exactly right, because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two war horses. Thus, we have the answer to the original question.

Now the extraterrestrial twist to the story...... When you see a Space Shuttle sitting on it's launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs. The SRBs are made by Thiokol at their factory in Utah.

The engineers who designed the SRBs might have preferred to make them a Bit fatter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, ..... and the railroad track is about as wide as two horses' behinds.

So, the major design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ass.

And you wonder why it's so hard to make things change ...



Thank you for an excellent (and elegant) summation of the issue.


Wonderful tale! Now, THAT'S the way history should be taught!  butelja, you have made my day.

Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.


And I'm still confused.  Many things are mis-named.  The much used kilo-byte is actually 1024, not 1000.  Computers are all digital - two states, on or off.  The popular numbers used in computers are 256 - 2 to the eighth power, 512, 2 to the ninth power and 1024, 2 to the tenth power.  Maybe we are supposed to have contradictory systems and numerous conversion factors.  As pointed out, many Imperial measurements are based on observations - horse power, the approximate length of a human foot, the width of a horse's behind, whereas the metric system is based on base 10, which nobody learns until they go to school.  Hmmm...



You're right, Blacksmity:  many different systems - and that's why we get the really big bucks, eh?  Canadians can't talk about a 2x12 anymore.  Instead, we are supposed to know that it is now officially a "38x286".

But, at least within systems there is concerted movement toward standardization.  In Medieval Europe, Ive read that each fiefdom (and sometimes each village within each fiefdom) had its own pole in the village square.  On this pole was marked out yards, feet, and inches, etc), taken from the royal foot of a visiting local king at some time in the past.  Each house-wright within the village district worked to the same measure, but woe betide a tradesman from another area - his measuring tools would be useless.  

Of course, measures are not for everyone.  Years ago, I hired an "experienced" carpenter to give me a hand framing.  He was to read out lengths to me, and I was to cut to size.  As I was waiting for the first length, I heard him mumbling to himself, and he finally called out, "Eleven feet, four inches...and...seven of those tiny little lines."     sigh.

Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.


Sorry to burst a bubble here, but ... From "TruthorFiction.com" on the story of the width of railway tracks:

This story is a "We've always done it that way" tale.  It says that the  standard distance between railroad rails in the U.S. is four-feet,  eight-and-a-half inches.  Why?  Because that's what it was in  England.  Why?  Because that's the gauge the tramways used  before the railroads.  Why?  Because the tramways were built using  the same tools as wagon-builders and that's how wide the wagon  wheels were spaced.  Why?  Because the old roads in England had  ruts that the wheels needed to accommodate.  Why?  Because the  ruts were made by Imperial Roman chariots.

The Truth:  There is no evidence that we could find that this is true.   In an article on www.railway.org by D. Gabe Gabriel says this tale  has existed since shortly after World War II but that history does not  support the claims of the story.  The Roman ruts, according to  Gabriel, were not for chariots but for narrow, hand-pulled carts.   Although there are many places where the ruts are visible, Gabriel  questions that they played a role in English railroad standards 1400  years after the last Roman legions.  One of the claims of the eRumor  is that the width of the ruts was affected by the need to make the  chariot and it's wheels the same width as the combined rears of the  horses pulling them.  Gabriel says there's a statue by Franzoni in the  Vatican museum that is regarded as the most accurate known  depiction of a Roman chariot.  The two horses are wider than the  chariot and the chariot wheels behind them.

Where did the four-foot, eight-and-a-half-inch standard originate?   Gabriel says it was from a Englishman named George  Stephenson.  Carts on rails had been used in mines in England for  years, but the width of the rails varied from mine to mine since they  didn't share tracks.  Stephenson was the one who started  experimenting with putting a steam engine on the carts so there  would be propulsion to pull them along.  He had worked with several  mines with differing gauges and simply chose to make the rails for  his project 4-foot, eight inches wide.  He later decided that adding  another six inches made things easier.  He was later consulted for  constructing some rails along a roadway and by the time broader  plans for railroads in Great Britain were proposed, there were  already 1200 miles of his rails so the "Stephenson gauge" became  the standard.

Interestingly, the 4-foot, eight-and-a-half inch width has not always  been the standard in the U.S.  According to the Encyclopedia of  American Business History and Biography, at the beginning of the  Civil War, there were more than 20 different gauges ranging from 3  to 6 feet, although the 4-foot, eight-and-a-half inch was the most  widely used.  During the war, any supplies transported by rail had to  be transferred by hand whenever a car on one gauge encountered  track of another gauge and more than 4,000 miles of new track was  laid during the war to standardize the process.  Later, Congress  decreed that the 4-foot, eight-and-a-half inch standard would be  used for transcontinental railway.

updated 5/30/02

Patricia Lougheed


Technically superior to my answer, but not nearly as entertaining.


Call me gullible but I'm still not going to completely discount bujela's tale until someone actually finds some old cart ruts and measures them, if for no other reason than it makes me smile. Besides, for all we know Stephenson measured some ruts on his way to work that morning. I also seem to remember something about the Romans (or was it the Chinese) setting a standard wheelbase for the empire to ensure their armies could move easier (of course my brain has been known to occasionally create a 'fact' to support a pet theory).


I design in english units because I have a feel for them.  My co-worker from Germany converts my answers to metric, so he can understand them.  I convert his answers to english units.  We create our drawings in metric units.  The machinist on the shop floor recalculates the dimensions on the drawing to inches because his measuring devices are in inches.

I guess we will all be metric when time is measured in units of 10.


This is a very interesting discusion, and I particularly like butelja's take on the matter, though that may only be becuse I am half drunk.

I am a Canadian electrician, who is having a bit of an identity crisis.  The code book I follow is slowly converting to metric; the most recent version gives all dimensions in metric, followed by imperial in brackets for those of us who still think in inches. eg 1000mm (36").  It isn't an exact science :).   When I order wire from the wholesaler, it's in meters.  When I figure how much wire I've used on a service call it's in feet.  The project I'm currently on gives the arcitectural dimensions in metric, and the electrical engineer has mostly followed suit, but not always.  So, I have a light that is centered between two doorways, 2600mm apart, and 9'8" off the ground.

I'm not sure if there is any point to this story, but it should show that with a bilingual tape measure I am pertectly comfortable working in any unit people throw at me, and I don't think twice about it.
If people can fluently speak more than one language, why shouldn't they do the same with numbers?


Good comment Richard7.

Patricia Lougheed


Of course there is the issue of safety also. People are less likely to make mistakes when they are 'singing from the same hymn sheet'.
I'ver heard a few horror stories such as a ground crew putting the wrong amount of fuel on a people carrier because they mistook metric with imperial.



My reasons for universal use of SI units:

1) pound-mass/pound-force is the worst abomination ever used in an engineering field.

2) kilogram mass can be directly linked to the periodic table and atomic masses.

3) the link between electromagnetism and mechanics - how would one use inches and pounds with volts, amps, etc.?


In an earlier post, I mentioned the loss of a NASA space probe (turns out it was worth $125 million).  For more information on that disaster, and many of the interesting newspaper articles that ensued, try going to


Interstingly, many of these articles blast the U.S. for not converting to metric.  In the same article, they blast the NASA and Lockheed engineers for making such a stupid mistake (i.e., not converting into one system or the other).  In my mind, that mistake is much more stupid than the US refusing to switch to metric.  Another interesting site defends the US's use of the English system:





Engineers are, axiomatically and at least: closet-trekkies ... therefore we all know where we going regarding measuring systems.
Live long and prosper!

(This pretended to be the Vulcan greeting).

Now, the amount of information that has to change (specially road signs, maps, scales, etc...) is so humongous that nobody is willing to accept the cost.
Also, the US version of the imperial units is called Std. e.g. the imperial gallon is different from the US gallon...why this does not surprise us?

o-) (smiling cyclop)


Beware the non-standardization even within an existing system.  I once encountered difficulties with installing new, fabricated in place, brake lines on a vehicle that I was restoring.  It seems the number of threads per millimeter on the vehicle (German) were different from the number on the tool used for the lines (english) even though both were fine pitch threads!  Not wanting to subject myself to leaking brake lines, I had to search out the correct components for connecting the lines to the vehicle.


Does anyone know of any good publiclications like the machinery handbook in metric?



I have Crane's Technical Paper 410 "Flow of Fluids" in metric (and english).  It's available on their web site.

Patricia Lougheed


When I read the story of the NASA space probe being mis-directed, it sounded like one company was giving data about the characteristics of the equipment they supplied (a thruster, I believe).  Another organization was using that data to compute how long the thrusters were to be operated to tweak the course as the craft made its way out to the target plant.  By the time the craft was near the planet the course was too far off for the limited power in the thrusters to correct the course.

The "how much thrust does this device generate" was given as a number with no units of measure attached.  (like:     thrust=27)

The other group seems to have assumed that the unit of measure was metric but in reality, it was English or Imperial or US or whatever name is most popular at the time.

The problem is that a number without units of measure attached means nothing.  It has no meaning in the world of physical objects or phenomena.  So the REAL problem was not that one party was using one system of measurement and the other was using another system, but that the first group supplied a number without a unit of measure and the second group didn't DEMAND that the unit of measure be supplied.  They just assumed something.

Some time ago, the owner of a company I worked for had this little saying.

"Don't assume anything, ..."
   (and at this point he would have already written ASSUME on the chalk-board)
" ... because when you do ... "
   (then he drew slashes on both sides of the "U" in the word -  ASS/U/ME)
" ... you make an ASS out of U and of ME!"


Well here in the UK you can see some beautiful drawings designed to confuse, i have seen many drawings marked in both Metric and imperial, now thats confusing.

When i was at school, i was taught only metric measurements,because we were told that the whole world worked in metric and we had to learn the new standard, and when i left to start an apprentiship you could see in the training centre about 100 faces in total blankness as the training officer spoke about inches and 3/18ths. So it just goes to show that what academia want and what industry gives are two different poles.


My car runs 53 stonethrows a mug diesel.   :)

We must accept that engineering is a multi-cultural environment.

It's just like understanding different languages.

I hope that we are all smart, reasonable and patient PEOPLE (!) here. And that we can easily deal with it.

- peace, Doryan


I do hope some-one buries a copy of this thread in a time capsule somewhere.  It should be good for some raucous  laughter in about 50 year's time.  Mind you, the designers/builders of the Tower of Babel have a lot to answer for in establishing so many different systems of units around the globe.

There are some beautifully fallaceous arguments for maintaining a status quo to be found in this one thread.

eg "the amount of information that has to be changed is humungous...that nobody is willing to accept the cost".  But some countries have accepted the cost.

Having made the conversion, it didn't seem any big deal in Australia (where, surprisingly we do have road signs and maps etc).  Granted, pipe fittings and the like largely remain non-metric, but they are not generally nicely 'imperial' anyway (other than threads/inch, how many of the thread dimensions are good looking numbers in either inches or mm?)  Similarly wire gauges, which have always been a total mystery to me anyway.

Personally I find dynamic calculations very much simpler in the SI system.  All I need to bear in mind is the definition of a Newton force (the force which accelerates a mass of 1 kg by 1 m/sec^2), and all is clear.  No more having to remember the nicety of pounds, poundals, slugs, the gravitational constant or whatever.  

I, like many others of my age, went through a period of wondering what on earth my design calculations in SI units really meant, and whether the results were reasonable. (When I first read 'Newton' in technical papers, I was inclined to believe that it referred to a New ton - yet another sort of ton, to go with the long, short and metric tons !).  But that passed quite quickly, and I would hate to have to return to imperial units again.

And for those who hanker for 'human derived units' - what would be more 'human' than to name the SI force unit after the 'inventor' of gravity, and make it equal to the weight of a British Standard Apple? (About 10 to the kilogram, 4.5 to the pound)


Cheers Austim!

That was brilliantly put. I liked, particularly, the time capsule thing. Indeed time unit is invariant to any system of units (although I know some units other than hours, minutes and seconds but they are not in vogue now).

But are you soothsaying common units in coming 50 years?

I totally agree with your point on threads and wire gauge.

But disagree with 'invention' of gravity, for before that too, people never used to fall down(?) on earth(oh no! can't exactly make my point)

Anyhow I vote for SI units.

I wish you a happy retirement life. (I read it in one of your other (great) posts)


Repetition is the foundation of technology


It must be a difficult issue when going down to details because some products are design and developed in US and manufactured over seas.
The jobs done in US have to go for english units because most vendors are in this systems.
But the production over-seas usually use ISO systems.  The exchanges between two systems sometimes causes terrible problems not only in accuracy but in parts supplies.
Currently, we are using dual-dimension systems.
Sooner or later, we have to face the globle-village situation.  For now, it is just in transition between.


WOW, I have enjoyed reading this thread and wish to add my bit to the time capsule.  As a teacher of engineering to entry level students, apprentices and Diploma students for 15 years I can vouch for the simpler metric system.  A 10 base is easier for students to follow, with a system of prefix's and by the use of engineering notations (+ve and -ve) and keeping their answers to within 1 and 1000 also makes for nice looking figures.

We still mention imperial however, here in Australia, because many countries still supply machinery and equipment to this standard.  The generation gap in some workshops still hear the older tradesman telling the apprentice to make it a few thou(imperial)over the 25mm size to allow for a press fit.  

The duoppoly of systems has lead to catastrophic outcomes and surely it is about time the engineering industry united to say "Metrics the Way - nothing else from this day!"     

Let's say, Jan 1, 2010 to give us fair warning!


It would be a great service to the World if some person or agency could convince us all use the same unit system. It will likely happen a few centuries after world government is established.

My doctor said I should take a thousand milligrams of vitamin C per day. I said isn't that the same as a gram? He wasn't sure.


I'll throw in two good stories about units problems--

While travelling from Michigan to New York (which all Michiganders know takes one through Canada), we left the
US at 28 degrees. As we switched to listen to a Canadian radio station, my wife remarked how much colder it had apparently gotten in the last few hours, as the temperature had plummeted to -2.  (She figured out her mistake when I about lost control of the car laughing).

While working at Opel, I was on the Proving Ground and a German engineer showed me a paved ramp (often proving grounds have ramps at various angles for a variety of tests).  The ramp was clearly not in use. He explained to me that they got the spec's from the US and diligently converted the length of the overall ramp from meters to units.  Somebody overlooked converting the height (from inches/ft rise/run), and ended up building the ramp in inches/meter (thinking it was cm/meter). After the meticulous construction was done, their slope was off by 1/2.54. They decided to leave it that way as a cautionary tale . . .



I'll through my 2 cents worth in on this one too.  
If I'm not mistaken the US government offically adopted the metric system over 100 years ago. Its the US businesses that are dragging their feet. Most of us here would be willing to accept the change, except for the cost.  I personally prefer working with base 10, the math is much easier. Eventually we will all be working with the same set of numbers, but that will probably take another 50 to 100 years.

Now for the funny stuff,  My wifes Toyota has a standard oil drain plug, My Chevrolet has a metric oil drain plug so does my Ford.  The Toyota was built in the US, the Chevrolet in Canada, and the Ford in Mexico.
The 'cup' of coffee I bought on the way to work this morning held 24 ounces, thought it also could have held 12, 16 or 20 ounces also.


I was changing a wheel on the Alaska highway last year and was attacked by a killer pascal.


Well, I'll offer this much.  I'm only 6 years out of college and I'm much more comfortable with English units that metric.  English units are based on "real" things where metric seems to be pretty arbitrary.  I can walk down a line and get a pretty good estimate of how many feet I'm dealing with.  I can't do that with meters.

I can see where students would have an easier grasp of metric in college, after all, those are all arbitrary problems and a student w/o experience doesn't really have a feel for what the numbers mean.  Is 20,000 lbs/in a lot?  Is 1 kilopascal a lot?  I know those answers now, but 10 years ago, they were just numbers.

And, I doubt that the US government adopted metric at any time, much less 100 years ago.  If that were the case, all the road signs, particularly on the interstate highway system, would have had kilomter markers instead of mile markes.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.


In truth, practicality and feasibility will determine our future course with this matter, as they should.  There will not be a need to switch the U.S. to metric until it can be incontrovertibly shown that the benefits of such a change will outweigh the costs (nickels per slug?).  

Speaking of which, there's another discrepency between nations that hasn't yet been resolved, and I contend that it's because the discrepency doesn't need to be resolved: we have different money all over the world, yet we transact international business with nary a glitch, because everyone is used to accomodating for the differences in monetary value between nations.  

I say the people who are worried about conducting business with the U.S. have as much valid need for concern about measurements as they do about being over/underpaid for goods and services exchanged.  

Seeing as how many different nations do business in the world today, and that there is a different exhange rate between every two that use different currency, AND that those rates change over time, it seems trivial to me that the static set of conversions between English and SI is such a burden.  Let those who work with their own units continue to work with their own units, in the interest of pursuit of quality (which is, I think everyone will agree, the fundamental purpose of engineering).  

This brings be back to my initial point:  Where the world stands today, there will be no crucial benefit to either party if the United States switches to metric.  If the rest of the interested world is willing to risk poorer product from the U.S. until it finishes the potentially lengthy adjustment, then go ahead and pursue the change... but there are enough level-headed people in the U.S. to realize it is not a worthwhile task, and I wouldn't expect much more adjustment than has already been made.

The solution to this problem, in my mind, is to overcome the perception of a problem.  

If someone needs a unit converted, then convert it.  It is far simpler than abandoning a perfectly good system for those accustomed to using it.


Another thought about the last sentence of my previous thread:

If an engineer was presented with two possible solutions to a problem, one complicated and one simple, and there was no solid proof that one solution was more complete than the other... which would he choose to implement if he was a good engineer?


Thanks for the link, doc11.  Still, when they start changing the road signs to be in kilometers for distances and kph for speed, then I'll believe that the government is serious about metric.  Even when they do, I'll still be having to make the conversions to figure out how fast I'm driving and how far I've got to drive.

If this USMA wants to get serious about bringing metric to America, they're going to have to do it through the media.  Never once have I seen a weatherman on any TV station give out the weather data in anything by English units.  If the news stations were to start using dual units in their reporting, with say, the next three years listing English/Metric and then switching to Metric/English, in about 10 years, you might have enough public awareness to put the English units away.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.


Plant experience has shown that the dual units approach does not work. You need to switch cold turkey and plan on losing a generation along the way. The good news is that most old people will just drive faster when they see that the speed limit has been raised to 100. This benefit tends to offset the fact that they no longer no how to buy food or tell the temperature.


I always thought that the imperial system was a better system especially when using units to the base 12 (inches and pound[currency]).  It was easy to divide things between people for barter for instance (1x12, 2x6, 3x4)... but now we have grown beyond that using mathematics as a tool for many aspects of life.

We have adopted a base 10 for our counting so it is logical to adopt a base 10 for our units (including money).  If we had a choice I would vote for a number system either binary or doudecimal (12) and from that would evolve the units.  But what advantage would that give in the conversion...it would never happen. Just like the campaign to have 13 months in a year (each month with 28 days... each month starting on Sunday ..your birthday always on the same day of the week)....It will NEVER happen.

We are stuck with decimal so currency and units should be base 10.  By the way I come from Australia where we have been through decimialisation in both currency and units in my lifetime.  Onwards to the next big step... which side of the road should we drive  or how to divide a circle... 360, 400, radians, 100 or?.



Engineers are Scientists.

We should use SI units for our work and be fluent in them.

We should also be able to speak to who we have to, and be able to explain what we want to whomever we want.

Which we should also learn to speak 2 or 3 languages other than our native language.

We should be able to solve any problem given any units.

SI units should be our preferred system and the one we encourage our children to learn and the system for all government projects and those projects who combine the talents of members from multiple nations.  It is the only thing that makes sense.

If we are waiting for someone to lead us...who do think it is going to be?

We are the leaders!


Escher - One you have SI'ed the circle and pointed a few rockets in the wrong direction, you will be ready for the SI clock and calendar.


Owg - We have split up the circle into 360 degrees basically since the Sumerians adopted a base 60 and as surveyors we split up the degrees by further 60 subdivisions (minutes) and again (seconds).  We repeat this in organizing time (seconds and minutes again).  So there could be an argument for base 60.

Which way to face the rockets? Well I hear that many military use the grads (400 to a circle) which is all a foreign language to me.



Get familiar with gradients, radians, degrees, minutes, seconds, vectors.  As an engineer, you are responsible to know these things.  All it would take is 1/2 a day with a good book - now what's so hard about that?

You may argue, "my expertise is Structural".

Because that is true does not negate one's responsibility to the profession to at least be casually familiar with units used in other genre of the same profession.

Come on, we are engineers, we are supposed to be smart, let's at least start acting like it.



Engineers are not scientists.  Scientists do research w/o care or consideration for what to do with the knowledge.  Engineers use that knowledge to create useful stuff and solve problems.  I would resent being called a scientist.

An engineer who says he can solve any problem is lying, or dilusional and should not be trusted.

And, why is it that we must all get behind this universal language of SI units, yet we must all learn other languages to speak.  If we're all supposed to line up behind SI, why not a universal spoken/written language as well?

I must confess, your two posts in this thread look like some pretty odd ramblings to my eye.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.



Thanks for your review.  I do tend to ramble.

I think a universal written spoken language would be great.  We are part way there with English.

Pretty soon we can finish the tower of Babel.

Any takers on who gets to be Nimrod.


Where do I sign up for the Esperanto class?
But seriously, we are arguing semantics as to whether or not engineers are scientists.  We do applied science. As to the statement that "scientists do research without care or consideration for what to do with the knowledge", I have known many the engineering academic for whom the same could be said. (And conversely the "scientist" who would bristle at the suggestion that this statement applies universally to his field)

I agree with Massey that we should all be casually familiar with all sets of units.  I would also expect that anybody with a formal engineering education in Britain or US already is casually familiar.



I was rambling about grads (an angular measure)  not gradient (a slope akin to the Tan of the angle).  It seems all those years at school learning about pennyweights, bushels, rods, guineas & fathings, chains, gram, litres (liters, see I can at least spell another language) reams, quires, US gallons, BTU’s, calories and short ton were all not in vain as my spreadsheet converter cannot handle many of these.

Can anyone out there tell me why there were 100 links in a chain?  It seemed like quite a sensible (land) measurement unit to me.


I'm not sure if this answers your question but:

1 mile = 8 furlongs or 1 furlong = 1/8 of a mile
There are 10 chains in a furlong
There are 100 links in a chain
That makes 8000 links to a mile
These are all exact so 1 link = .66 feet exactly.

Compared to most of our other English units of measurement these are pretty easy to remember.  It is almost even intuitive.

I know this doesn't directly your question but at least all the numbers are non-fractional which would have been very convenient to use given the time they were invented.


Escher - 100 links in a chain appears to be early use of the metric system by surveyors to make the math easier.

Try to think of a contraption to make your life easier; do your survey work faster and with more precision. After all a 6.5' wooden stick is very cumbersome in the countryside. One of these sticks was called a perch, it has also been called a pole or a rood and most recently in the United States, a rod.
The answer came in the form of a metal chain. The first 16.5' chain with one hundred links came about in England around 1620. Shortly thereafter an English inventor and mathematician named Edmund Gunter designed a more useful "chain". Gunter, being number-oriented, devised a system of land measurement around his "chain."

One Perch = 25 links = 16.5 feet.
Four Perches = a chain of 100 links = 66 feet.
80 chains = one English mile = 5280 feet.
10 square chains = one acre = 43, 560 square feet.
This system worked very well in early America with the vast expanses of land to be surveyed. Because of these vast expanses acreage was easy to compute. Just multiply length times width in chains and links (1/100th of a
chain) to obtain the number of square chains. Then move the decimal point to the left one digit for the amount of acres.

Example: 20.68 chains x 40.17 chains = 830.72 sq. chains or 83.072 acres.
  100' Engineers Chain  
Made by Chesterman - Sheffield, England circa late 1800's
100 open links, 2 rings per link, 1 swivel, 0.16" wire, cast brass handles, not adjustable.
Tally tags at +/- 10, 20, 30, 40 and center on side rings.  
 Another advantage of Gunter's chain was his system of counting links. A round brass tag was placed at the center 50 link mark . And from each end every 10 links were marked with a brass tag and pointed fingers to match the number of 10 link increments.

Well, you asked.


Perhaps we should defer the changing of all US road signs to SI units. At some point in time they will be obsolete since speed limits will be available on board based on GPS. Looking to the side of the road and spotting an occasional road sign is a primitive method of speed control.

In Canada, as part of a concerted effort to run up a massive debt, we converted all our road signs. These road signs will be an interesting feature for tourists to smile at, just like the milestones at the roadside in England. I haven't spotted any meterstones but I will watch out for them.

HAZOP at www.curryhydrocarbons.ca


The best thing I like about metric is that 1 cubic meter of water weighs 1000 Kg! And considering value of acceleration due to gravity is go close to 10 (9.81 actual) it makes it 10 KN. Its like magic!!


According to this site: http://www.ex.ac.uk/cimt/dictunit/dictunit.htm#standards the following rules apply to the use of numbers in the SI System.

"To make numbers easier to read they may be divided into groups of 3 separated by spaces (or half-spaces) but NOT commas.
The SI preferred way of showing a decimal fraction is to use a comma (123,456) to separate the whole number from its fractional part. The practice of using a point, as is common in English-speaking countries, is acceptable providing only that the point is placed ON the line of the bottom edge of the numbers (123.456) and NOT in the middle."

There seems to be no pre-set way of setting up Excel to use this system, although Format, Custom, can handle it. Do SI fans use this system or just ignore it.

HAZOP at www.curryhydrocarbons.ca


How many companies do you know that did this when they converted to metric? They took their english dims, say there was a part that was 3.75 inche long, it is now 95.25mm.

I am getting use to working in metric in the Motion Control world. The problem is that every customer seems to work in different units. in, ft, mm, cm, m..... one mfg list specs in kg-m^2, then next in kg-cm^2, the english in lb-in-sec^2 and oz-in-sec^2.....

This is why all of us need that 500 page book full of unit conversion tables.

In Motion Control, when some one asks for a 36" stage, they get 900mm (35.43 inches). I see this a lot too: Give me 300mm of travel and English mounting holes.

I'm sure the state patrol would love it, changing all the signs to metric. All of us going 100 mph when we are suppose to be going 65 mph (100 km/hr).

Cameron Anderson - Sales & Applications Engineer
Aerotech, Inc. - www.aerotech.com

"Dedicated to the Science of Motion"


With regard to road signs, I was in Ireland the other month and many distance signs are Metric and some still imperial.  The Metric are white on green, Imperial black on white.

No problem in the small Toyota hire car I was driving.  All the display was LED... speedometer, odometer, trip computer....and there was a handy button which allowed you to switch backwards & forwards; metric or imperial as you feel inclined.  Of course you had to remember the speed limit (posted in metric) so Metric was my preferred option especially in speed zoned areas.

While I had no problem driving cars with imperial speedos for about 8 years after we converted (Australia), it seems like a good marketing ploy for vehicles that may be taken to different countries.

Another innovation (to me) was a big transparent sign on the windscreen reminding you on which side of the road you should be driving.  Of course the steering wheel was securely mounted on the right.



You can change the settings for number format for all windows applications.

Contror panel then regional settings and put in the number, date and currency formats that you need.

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion


Living Canada I have long accepted US or Imperial gallons which ever the design called for.  But if US does not use Imperial what does it use, and by the way Enland uses (mostly) metric not "English".

The one I find hardest in US is why report metal production (such as copper) in million pounds/yr.  Why not tons.  I see there is now a move to update this to millions of kg/yr again why not tonnes.

Just for one last confusion.  In Europe they don't use decimal points but a decimal comma.  So next time you see 1 234,56" it might not be a typo, comme il faut.


One sure to convert the unconverted from 'english' to metric units is to have them take 'Dynamics' class in college.

After a few attempts trying to calculate accelerations using 'slugs', almost everyone converts original information to metric units.  Then if the answer is required in 'english' units, it is converted from the 'metric' answer obtained working the problem in usable units.

Slugs is a good name as it is indicative of engineers who are too stubborn or 'sluggish' to use the only international system of units that makes sense to use.


RDK, thanks for the tip on using Control Panel. I guess I was not thinking outside of the box.

HAZOP at www.curryhydrocarbons.ca


As a supplier to many automotive industries some times we come across funny drawings.One major US auto company the drawings are in metrics and suddenly we get another print which are all in inches one has to look for clerks table to understand what it means.the biggest problem is for the us companies only because most of the standard parts for the components all over the world are in metric system and it is impossible for the US companies to get some standard ittem which is non metric.for example the standard shaftat could be 8mm diameter and the other mating parts you can easily get to match that.This is not the case otherwise and one has to ultimately turn to metric system since majority of the supplies to US are from countries like china are metric based.


As Escher mentioned, here in Ireland the signage is in kilometers(this crossover has been going on for the past number of years and is not yet fully complete). However, the speed limit signs are in miles per hour and continue to be this way. I think, Escher, you had a leisurely drive around the country if you believed the speed limit signs were in metric.

Another example, myself and a friend of mine, who is from South Africa entered a 10km road race about two years ago in Limerick. All the adverts and pre-race publicity talked of a 10k road race. When he got to the '5' marker, he thought his performance on the day was very poor, so he started to up the pace. Soon afterwards, he saw the finishing line.....yes, the markers were in miles!!!

Yes, it's a funny old world...


As Escher mentioned, here in Ireland the signage is in kilometers(this crossover has been going on for the past number of years and is not yet fully complete). However, the speed limit signs are in miles per hour and continue to be this way. I think, Escher, you had a leisurely drive around the country if you believed the speed limit signs were in metric.

Another example, myself and a friend of mine, who is from South Africa(metric system is in place there on infrastructure) entered a 10km road race about two years ago in Limerick. All the adverts and pre-race publicity talked of a 10k road race. When he got to the '5' marker, he thought his performance on the day was very poor, so he started to up the pace. Soon afterwards, he saw the finishing line.....yes, the markers were in miles!!!

Yes, it's a funny old world...


Well, for those of us in Canada (and anywhere else...) that have to live with both US and metric systems and may have trouble with conversions, here's a little tool to help out.


Let me add my favourite to this interesting discussion:

Measure in micrometres, mark with chalk, cut with an axe ;)

ps: as you see I favor metric... (using 1/16th of an inch is killing me!!!)



I agree with many that believe that the metric system is simply easier to navigate (calculating volumes of concrete, MxMxM thickness easily gives you a volume, I worked in South Africa as an engineer and it was much easier than in the USA. I do concur with the mindset of Americans with their sq in, sq ft, acres, cubic yards etc. as a way of "mentally knowing the size, volume, etc.", this will not go away anytime soon, unless the US gov't, as in other countries merely insist legally the use of metric. I don't see this happening soon.


For some time fluid density meter manufacturers used the SI convention to express accuracy. e.g. +/-0.1kg/m3.
Then came the day the coriolis mass meter manufacturers decided to target the density measurement market. As mainly american manufacturers they decided to quote not lbs/ft3 as they usually did but to use g/cc. e.g. +/-0.0005g/cc. For some reason end users seemed to think +/-0.0005g/cc was more accurate than +/-0.1kg/m3 so then the density meter manuafacturers had to follow suite and now quote +/-0.0001g/cc except for fiscal metering where they may still quote kg/m3.
And who said its easy enough to convert between one system and another? what happened to the Hubble telescope?


I for one do not believe the hubble or mars probe errors are due to conversion errors.

I an not generally given to conspiracy theories, but I do not buy into scientists and engineers making conversion errors or forgeting to convert  or whatever.


Conspiracy theories? I don't believe i made any mention fo such. I was talking about being creative/imaginative with the figures ("lies, damned lies and statistics" sound familiar to you?). You are probably right about Hubble though, and though the Hubble news centre doesn't exactly give anything away, they don't assign a cause to the problem. According to other sources they finally assigned the blame to an incorrectly assembled test instrument. I just recall the original news coverage in the UK suggesting (mischieviouly?) that the cause was conversion factors.
Of course i have as much or as little difficulty believing a scientist or an engineer can miss-assemble a test instrument so it is only 1/50thou off as i have about them making conversion errors. If i "miss-assembled a test instrument you can bet if could bet it a meter or more off.
I have no reason to doubt the official story but it wouldn't surprise me if at some time in some similar situation some one hasn't invented some less embaraasing story to tell the public than the real truth.
But this is about engineers and scientists not making mistakes...i am reminded of the old carpenters adage... measure twice and cut once. i.e. we are all fallable and we are most fallable when we decide we are infallable and measure only once. Hubble is the proof of the ability of engineers to err and it really doesn't make much difference whether it is because they can't convert or they can't follow the assembly instructions properly. (And who reads the instructions these days...? and there is another problem... with assembly instructions required in multiple languages today, the actual content has decreased to a meaningles legal minimum). The main point is that if we have to make conversions we will make mistakes. It is an unnecessary step, or at least, one which can be eliminated while i doubt we can eliminate instruction manuals or make them readable and helpful. If conversions have to be made i don't care who it is, sooner or later human beings will find a way to foul up. A lot of engineering today is about is making things "idiot-proof", the newer your computer the less decisions it allows you to make..."plug and play", "straight from the box"... and so on progressively eliminating any possible areas where people can mess up. And if you think engineers can't mess up a conversion then you won't prove it by my colleagues and I. Take the example i gave, we were caught out in one of the factors we quote because we got the too few noughts (zeros) in the specification; not one engineer, but several, the guy who wrote it up and the guys who checked him.


The Metric System is a modern system devised to be a coherent system of units.  The other system of abitrary values devised by the UK/GB and adopted/adjusted by the USA is simply a museum piece and a pain in the proverbial to use.

In defence of the 'old' sytem it suited the measurements expected at the time; chains, furlongs, slugs, pounds, ounces etc.  Not so much these days.

I don't think there is any argument for the old system except that old fuddy-duddies, (do you have that expression in the US? It means anyone old and boring in the UK - hey not my definition. I qualify as one), like to be able to demonstrate their ability with it.  They are dying out though!

Come on you guys join the real world and dump the inch/foot/slug world.  No one says that you can't still specify cycle threads for; err, umm ... cycle applications.  Or Unified Fine for whatever.  Some of those applications will continue to be relevant - we still make Whitworth and BSF bolts and nuts.

It's easier and more sensible ..... till the next one!


Has anyone given any thought to the cost to replace measurment instuments and such, most of which must be provided by the machinist. While I agree that it is easier for engineering to use metric, this is not true for manufacturing. I didn't whine when metrics was implemented and I had to convert them to decimal, why must it be your way.


JML has pointed out that "The Metric System is a modern system devised to be a coherent system of units." There was an interesting documentary about the two French gentlemen who set out to define the meter as a fraction of sector of the earth. Unfortunately one got caught up in a war and got stuck at the latitude (I think in Spain) for the South extremity of the sector. Being the good scientist that he was he took advantage of the delay and repeated his thousands of readings, to verify his initial findings. Unfortunately he got a different answer so he did not tell anyone about the problem.  I think he just used the second set. Subsequent analysis has determined that that the error was due to wear and tear on his much used instrument. So we are stuck with yet another irrational basis for a unit of measure. Does it really matter? It turns out the earth is not as round as they thought it was then anyway.

I am sure others have further information on this piece of science history. I will be interested to see any additional postings which can correct/expand my recollections.

HAZOP at www.curryhydrocarbons.ca


Don't worry about the cost of the instruments to measure, what about all of the automated machines that are driven by imperial and their operators. It is logistically easier to teach technical people to convert units than it is to teach the ordinary person to convert units.

Although I grew up in an Australia that was converting to metric (DOB 1965) I am still amazed to see older people using imperial as their terms of measure (quite often converting from metric first!!). The real transition took about ten years of education via the education system as I can recall many teachers who simply refused to teach just the metric system. So I am lucky that I can now rapidly convert the basic units in my head.

The SI system is still the way to go but again not every one talks the same dialect. Here is a recent example of units that were available in an analysis program: kN/m^2, N/m^2, kN/cm^2, N/mm^2, kPa, Pa, plus three versions of imperial measure. The SI system as I understood it is designed to simplify measure to units of 10, with a means of reducing the number of numbers dealt with, ie: k for 1000, M for 1000000, etc. Why doesn't it seem to work in practice?



sc - Why don't we make better use of deca, kilo, mega, and their cousins deci, centi, milli, nano, pico, femto, atto, giga, tera, peta, exa? Perhaps it is because they are far from being a modern coherent set. Rather they are tributes to "the Latin", and a few recent heroes of science. Presumably they were named to avoid favouring either the English or the French language. At the time many of us studied Latin so that was a good choice. Its time to rename them based on ten hundred, thousand, million, billion, trillion, etc. Then perhaps we will stop selling cars with 200,000 km on them, and my doctor will stop prescribing 1000 mg pills.

As an old fuddy-duddy who will be dying out soon, I just thought a final outburst might make my 86,400 second day.

HAZOP at www.curryhydrocarbons.ca


The metric system is for lazy people who would rather shift a decimal point that learn to multiply or divide by 12 or 3 or 4 or 8 or 16 or or or or...   Just kidding.

as an american, I learned the imperial (suitably modified) measurement system, but having travled and worked in many other areas of the world, I had to learn the SI system.  Big Deal!

I don't convert.  20 C is 20 C.  32 F is still 32F.  I do find that a meter is too long and a gram is too small.

I find that engineers were smart to do away with inches and divide the foot into 10th's

Architects should do the same thing instead of foisting fractions on us.

to paraphrase archemedes...  "Give me a stick and I can measure the world."  I just have to hand THE stick to you so you can verify my measurements.

In other words, give me a system.  Tell me the rules. Then YOU stick to the system and the rules YOU gave me.  (and hurry, please.)


the thing that annoys me most, to refer back to a post from a fair way up the thread, is that "1 cubic meter of water weighs 1000 Kg"... that's the absolute stupidest thing about the metric system. now don't get me wrong, i'm a metric man all the way and think imperial systems are just a great invitation to screw up, but why is it that the metric measure of mass's base is a factor of a thousand out from the rest of it's units?

a cubic metre should weigh a gram... that way, ONE newton would accelerate ONE gram by ONE metre per ONE second!

WHY OH WHY is a gram one thousandth of the mass it should truly represent!??

now that i've ranted about my one major problem with SI units, i can start on my 59 major problems with imperial units...



Why not 1 mega gram. Isn't the SI system supposed to allow us to work in small numbers.

HAZOP at www.curryhydrocarbons.ca


If God had wanted us to go metric he would have given us 10 fingers - Homer Simpson


Again Homer is wrong to a certain extent, we have five digits per hand, giving us the metric world of 10 in total.




Greg Locock


i take it you don't watch the simpsons that much?

they only have four fingers (or three and a thumb if you prefer) per hand...


autocol is correct and I just wanted to post to support him, and Homer of course, Homer is never wrong!!!  I think Homer is a closet Engineer, Nuclear of course, now we know why nucler engineers are a little bit stranger than the rest of us!!!



autocol is correct, and so Homer has a good excuse, but others?


Sorry guys I don't watch the Simpsons at all since my wife caught my oldest daughter and I discussing the more stressful (for Bart and Homer) parts of a particular Simpsons episode and how it could be applied to her mum every now and then. So now it is banned whenever she is in the house.




The meter is no longer defined by the original measurements taken by the originators of SI, it's now defined by the length of a certain (Not very round) number of wavelengths of a particular emission wave for a particular atom (Haven't time to check out the specifics at the moment).

The same is true for the mass of the kilogram, the length of the second etc. They're all defined by atomic physics rather than the older more direct standards (IIRC the length of a metre and the mass of a kg used to be defined by the length of platinum bars held under atmospheric and temperature controlled conditions in France).

I would be interested in finding out why the kg is the fundamental unit of mass instead of the gram or rather why the gram wasn't assigned a mass equal to a kg first day. It could be due to chemistry calculations where 12g of Carbon 12 is equal to 1 mol of the substance, but I wonder does anyone else know.

Also, speed limits in Ireland are still posted in mph, with distances in miles on old signs and km or miles on new ones (Since people are happy enough working with either unit it doesn't really matter). Green signs are always km though. Temperature is always in Celcius, celcius is about the only unit in SI that really is easy to get your head around, 0 is where water freezes and 100 is where it boils. I've never used farenheit at all, though medical thermometers often use it.

I've worked in SI and Imperial/US units, and SI certainly makes more sense. Ireland still uses a mix of units, but the SI system almost universal for industry, except for the specification of wire gauges, pipe fittings and land areas.

Strangely enough I'll still give distances in inches/feet when talking to people but always work in m/mm on paper. Part of teaching people to work in SI does involve assigning every quantity in the calculation a unit and performing the calculations on both the numbers and the units to arrive at an answer. If this answer has the correct units then at least the form of the equation used is correct. The lack of fiddle factors in calculations is the real strength of SI I think.


peglor - Thanks for pointing out the current bases for SI standards. I think that the reason that the number of wavelengths is "not very round" is that it is chosen to equal the originally floored measurement. Perhaps we should have waited until the earth changed shape enough, then repeated the measurements when the wavelength number came out to be a whole number. The length of a king's foot still makes more sense to me on a cost/benefit basis.

HAZOP at www.curryhydrocarbons.ca


I believe that the real reason the USA resists conversion to metric is the manufacturing and business infra-structure.

Machine tools are calibrated in English units.
Pre-formatted programs assume English unit values.  For example, to make an entry in a catalog, I might enter the number 51.  The output automaticvally appends "inches" or some other unit to that number.  And, so forth.  

The education component can be dealt with over time.  The replacement of machines and programs, etc. can also occur over time but the result would be some machines on a shop floor producing in metrics and others in English units.  That is patently intolerable.  A means of cost-effectively managing the transition has not been devised.

Even if you consider a "green-field" plant, the transition is a problem.  If there is no market for metric widgets, then it makes no sense to make them.

So, in my view, economics is the problem; not education or arrogance or willfulness or the lack thereof.

If there was an economical solution, I am sure American businessmen would be pursuing it aggressively.


I've heard rumor that the metric system was the brain child of Napolean (although not French himself) and the US will never completely go metric because of it's (French) origin -- ha, ha...

anyway, it is a shame that our schools do not teach the metric system anymore than it does -- the fundamentals of understanding measuring systems really originate at home to kids before they even go to school -- we will need to have the parents comfortable in doing things normally in the metric system so the future generations will have an inate feel for it (I fully understand the system, but it is not intuitive to my thought process)... I specify all things in US Standard because all of my employees know it and few know the metric system... a ½" is obvious, 15 mm is an unknown...


"US will never completely go metric because of it's (French) origin -- ha, ha.". Since the US form of government is largely based on French ideals at the time of its creation I think that would be a strange argument.

Quite why such a piffling detail as the choice of measurement system creates so much angst is beyond me. All measuring systems are arbitrary, with the possible exception of integers (counting). Even then the choice of base is up to the user.


Greg Locock


My kid (a junior in a U.S. high school) told me I needed to cut 2 cm off a board - I hit him with the board of course.

I just retired from a global company and used to get some interesting unit references.  One guy in Canada asked if he could run 3 E3M3 of gas up a 2-3/8 string of tubing at 70C and 1,000 psig.  Someone in Indonesia had a problem with 6 miles of 4064 mm pipe.  etc.  The "E3M3" reference seems to be unique to Canada, I asked "why not km-m2?" and got a blank stare.

Things are changing though.  The post WAY earlier that said their Toyota had standard threads and their Ford and Chevy both had metric had a key bit of data in it - every auto mechanic in the US today has to have two complete sets of tools.  That's expensive and I believe that over time the "standard" system will vanish from the auto industry because of pressure from mechanics and unions.  They say in this country "as goes Detroit, so goes the nation" (or something like that) and not long after the autos stop mounting 16 inch wheels with 25 mm nuts, the metrification will accelerate.  We're already fine with 5 liter engines.

There's nothing inherently good or evil about any system of units - they are simply a means to describe the physical world.  The only evil in this discussion is the engineer who fails to specify units.  If we are rigerous in always describing what we mean then the opportunity to screw up in a big way is less.

David Simpson, PE
MuleShoe Engineering


The one thing that comes to mind in reading through all these threads and that's the value of carrying units through all your calculations.

The example offered of the space probe going off course could never happen if the units were carried through.

I was taught early on to check for dimensional consistency at the end of every problem. I didn't really start to do it assiduously until I started doing chemistry and balancing redox reactions.

That's the biggest problem with Excel and lots of other programs I've seen - they let you mix units invisibly.

Regarding the change over to SI, I don't think it'll ever happen in public commerce, highway signs, etc. The average American just doesn't care to learn a new system of units and there's nothing in it for any politician who'd care to take up the banner. There are much better sound-bite issues available.

I presume that all engineers and scientists are "dimensionally bilingual".


Congratulations to the Metric thread on reaching 100 posts.

HAZOP at www.curryhydrocarbons.ca


When I started at school, we were still on the imperial system. Then metrication raised its head and we moved to the c.g.s system. Before long someone decided that this wasn’t right and we shifted to the kg.m.s system.
To say we have the SI system would be wrong. As other contributors have pointed out, most people work with a mix of units drawn from different systems. Even using cm instead of kilometres isn’t quite the same as using the SI system (a centimetre may be legit as an expression of length but what about when you calculate volumes?  1 cm3 is not SI, 0.001M3 is. Or is it? Then too, should it be 100ml or 1decilitre? Then add to the confusion by changing the names. The move from Fahrenheit to Centigrade was problem enough but change the name from Centigrade to Celcius, and Curies to Roentgens or whatever and you can confuse people even more. And what is the difference between 25C and 26C is it 1C or 1C ? is it because 1C is an actual temperature and 1C (one centigrade degree) is a difference in temperature…. but who is rigorous enough to make this distinction?

Now if life were as simple as just changing the road signs then I guess we’d all be in one unified system already. The speed limits don’t matter since no one takes any notice anyway and they become self-funding. Just install any speed sign in whatever units and follow it with a speed camera. In fact, in Europe speed limits are proving such a money-maker they have introduced variable speed limits on the Motorways, Autobahns, Autostrada, etc.. So one minute you’re legal and the next they dropped the limit on you, took your picture and made a cool £40. But that’s a political move and politicians won’t do it. It might cost votes (especially after Chancellor Kole bought it for a double whammy of (a) 1Duetsche Mark = 1 Ost Mark and (b) getting rid of Herr Titchmeyer, the Deutsche Bank and the Mark altogether for the Euro.

But if you give any retail business the choice they’d say let’s change. Let’s have lots of changes. Let’s have one after the other and don’t let’s try to do it all at once.
They know that the secret of any change is that the consumer pays.
Take plumbing, it changed in the UK many years ago. And guess what, 12mm and ½” are close, but not close enough. Any plumbing job became a nightmare in the UK as it gave plumbers the opportunity to change out whole plumbing systems because the new and old copper tubing didn’t match. “Change just one bit and you’re storing up problems for the future” they’d say. “Better to do it all now. Don’t know for how long we can get adapters”.
And note that the various adapters always seemed to be unreasonably expensive. “special” ½” to 12mm adapters always being more than ½” to ¾” or 12mm to 15mm. Or even than 12mm to 12mm straight connectors.
Another example, changing the weights to “metric” required every manufacturer to change from 1/2lb blocks of butter to the new metric equivalent size. Guess what, I’m sitting here debating whether to go and look at a block of butter to see what weight it really is sold in here! It looks the same (or does it?) I don’t know. …….
……………and I still don’t know, the wife takes the wrapper of and puts it in a dish. There, I actually went and checked. I think it is now 250gm (not 0.25kg). Some things went to odd values like 454gms (a pot of honey). Why 454? Is that a direct conversion? I doubt if any shopper knows (and how can the manufacturer say that this is approximately “30 servings”.  The reason obesity is a problem is no one with an IQ of less than 180 can fathom out how many carbohydrates they’re eating per portion. Any diet is great but only if you have the first clue about how to measure your food factors. Food labeling is a nightmare.
While the poor consumer is struggling to figure out the difference between 1/2lb and whatever number of gms (250gm?) they now sell it in, they missed that the price per lb and price per kilo showed an amazing thing, it costs more when you buy per kilo.
Look at decimalization, (£1=240p to £1=100p) or any currency change. In Europe the coins have been withdrawn from circulation. Each one has been defaced. Then they have all been replaced with the new Euros. That costs money. I don’t know why they did it. It doesn’t make any sense at all, especially not for politicians except that each dreams of being President of Europe. But again, the consumer pays. Through taxation. Of course, some of the costs are recovered. The old coins are sold for scrap. One company in Scandinavia is turning them into ship propellers. I don’t know what other uses are being found. Who pays the balance of the costs? Helpfully, all those people with undeclared income stashed away in hard currency who couldn’t face walking into a bank with a suitcase full of old deutsche marks to trade for the new Euro (this was a serious problem in Germany, we are told) have helped contribute to the costs.
The currency change has, naturally enough, given the manufacturers another chance to hike the prices. Not just by rounding up when converting, this is small beer. For example convert 1 DM to Euros, it isn’t an exact conversion so naturally enough the sum is rounded up.
Now since many products are priced at $9.99 just to convince us its cheap where $10.00 makes us think it is expensive (I always fall for that one!); going from DM4.99 to E2.7445 goes to an intermediate E2.75 (a small gain) and then to a new E2.99 (a better gain). For the DM to Euro conversion notice that DM4.99 looks bigger than E2.99 because 4.99 is bigger than 2.99. This means it is easier to hike the price still further and hide it by fiddling with packaging sizes. So just change the package size and shape a bit and throw in a “Free” 20ml special offer. When the “Free” 20ml disappears no one will notice that the product costs 10% more after the currency change to before. Most people are pretty good at “size/weight recognition” when things are packed consistently. So always be sure to change the packaging. The fact that wine was sold in bottles where a bottle was 26floz was never a problem. It looked like a bottle. So just change to 75cl (not ccs) and change the bottle shape and who knows what they are buying?
More difficult is the conversion from Francs to Euros because the exchange is something like this: 4.99F = E8.2269. An immediate problem because 8.23 looks more than 4.99. Of course, the re-packaging trick works as well here. But while you may put less in the package to drop the price closer to E5, you may find it advantageous to not reduce the package size in direct proportion to the weight reduction. Buy an expensive box of chocolates some time and see what I mean. You’d be surprised what imaginative packaging can do to make 200gm of chocolates look like a 1kilo box, especially if the actual weight is printed just once in very small print.
So the trick is, never let the punter contend with just one conversion. Add a few more in and some repackaging tricks. There is even a fair chance some of them will get one of the conversions wrong, think they’ve discovered a big mistake of the manufacturers and stockpile two years worth of franks & beans. Then too, every change is an opportunity to sell $3 solar powered pocket converters at $9.99 a pop.
If you think this wouldn’t fool a 3-year-old, you’re wrong. My wife looks at the price per package and not the price per kilo (and shelf tags are very confusing since some show the price per kilo, some the price per 100gm and some nothing at all.)  When we are in Europe she still converts the price to DM and using a 10 year-old conversion rate via Drachmas into Stirling. This is her sequential approach. She works things out according to the sequence of countries she has lived in, making no allowance for exchange rate changes. This is no more flawed, financially, than the EU approach to the Euro. Naturally, we don’t go shopping together. I spend the time trying to work out the prices only to find that while every other Mars pack has a shelf tag showing the price per 100gm the bag of fun size bars doesn’t have this so I never can decide whether to buy mars bars or not. I mention this because when there was only one size of Mars bar, the Mars bar price was used as a simple economic indicator in the UK. Now we have the “Footsie Index”. She, meanwhile is buying two loaves of bread for the price of one when we can only eat one (the ducks get the rest) but they just don’t offer half price bread. And how many pairs of red shoes can she really use? (none, it seems. She likes to shop for them, buy them and put them in the cupboard. I have never seen her wear them)
Letting illogical beings do the shopping unescorted is no great way to survive but it keeps the peace (Is a female Vulcan a contradiction in terms? Most illogical) but this is the key to change.
So believe me, even with the dumbest of finance directors, CEOs etc any half-way decent marketing guys can show a dozen or more ways to milk any change of units, currency, or anything else for a minimum 10% premium. All they ask is don’t do it all at once because that’s a clear 10% premium per change! And hey! The decimal change was a great earner. Why not now try binary? I can count to 10 on my fingers in decimal but to 1111111111 in binary (1023 in decimal?)    The US has already started with a $1 (10000$) bill and a $2 (01000$) bill. They just need a $4 (00100$), $8 (00010$)$16 etc and we are half way there. Then label the old $5 bill 10100$ and the banks can get rich.
If we run out of changes, let’s do the whole thing over again, starting with the Babylonian hexadecimal system and cuneiform script. Bill Gates won’t like that, but I’m so fed up with having always to change the templates from Time New Roman to anything, anything else at all that Cuneiform will make a nice change.
So how about it? I’m game.


There are 10 sorts of people. Those who understand binary, and those who don't.


Greg Locock


Well, time for my rant on this subject I guess

Being French, I'm indeed using metric system since I'm a kid. I learnt it at school and I'm using it in my every day life.

In my student life, I happened to go one year in Canada for my studies. Hence I had to deal with all your series of units and transform my Francs/Liter (was before 2002) in US$/Gallon for the car gas during my trip in US for spring break. Heck of a story it was! I let you guys have fun with this without your comp nor your calculator, because of course you do not travel with any of those when you go in holidays, do you? To help, you can use 1 US$ = 6.50 Francs (was around this at the time) and good luck to calculate by head

Now, do I care to have horsepower or watts for my engine specs? not really. HP is an old unit and people are used to it. I agree we should switch to Watts in regards of SI units. But let's be realistic! What does it change for customer to have Watts instead of HP? The real use is for the engineer, isn't it? Leave customer use their HP, most of them wouldn't know what Watts are anyway. For them, Watts are only related to their electric bill lol.

We however, as engineers, have to follow codes.

You guys in US use alot ASME, FAA, IEEE or whatever codes to design, manufacture etc your products, don't you? So why in the Hell wouldn't you use SI units?

I know it's related to your History and culture, and thus you won't leave your units easily. Hence I don't ask you to abandon them, just to work with SI ones. Just as I work in French and English on my papers because those are intended to be used by many countries. Papers intended to be use only inside my company are written in French. Do you see my point?

There are standards set for international understanding, and as engineer, I think we are educated enough to apply them as well as understand what they are and why they exist.

Just my 2 cents

Cyril Guichard
Mechanical Engineer


Brilliant one, Greg! (You got me guessing.... it's like a null set. I understood your post but binary system is well over my head)

Believe it or not : There is a three dimensional figure but only with one face, called Mobius Strip.


This is funny. Why is it even an issue which system is used. Ok so we use english here in the U.S. and everyone else uses metric. Once you learn both then it's no problem to use either. I know there are a lot of advantages to using the metric system because it makes more logical sense. But think about in the english system where the 1 lb mass is equal to 1 lb force. I would guess that some people would argue that that is a nice system. Each system has it's advantages and disadvatages which makes me believe that both systems aren't going anywhere.


I am Canadian and born in '71.  I grew up during the introduction of the metric system and had many a blank stare as I entered the world of automotive manufacturing.  It took me about 6 months to become fully fluent in Metric and US units.  I know without hesitation that 1 mil is 39.37 thou.  And YES those extra digits ARE significant.  I know people who use 40 and people who use 39.  They are both wrong and have cost me tens of thousands of dollars in wrong parts for my machines.  I know people who don't know what a thou is and people who growl at me to use imperial "cause the lathe ain't metric".  I convert specs from lbf to Newtons and back again in my head these days(4.448 N/lbf).  I have two different sets of allen keys.  I know it is 454 g per pound and 2.2 lbs per kilo without thinking.

Bottom line here is that we are Engineers.  We by nature have to be multilingual in measurement.  Why you ask? Well when you are standing in front of a piece of assembly equipment the part needs to be long enough and strong enough to do the job. It really doesn't matter what unit you use to measure it.  

"The cylinder needs to have a 0.002485 furlong stroke and be capable of working at 4137.19 Torrs."  If the sales guy understands it great.  If not you just wasted another $1200 bucks.

Also even Detroit is not willing to shell out the hundreds of billions it would cost industry to immediately convert all their equipment over.  It would cost my current facility (1 plant of 500 ppl) just over 172 million to completely convert our equipment.  And I am sorry but I cannot come up with a 1 year payback to justify it.  And that is why many people still use the US units.

Oh yeah and butter here is sold in 454g blocks.


I have been an engineer for several years and have used both the metric and imperial units (my personal preference is the SI units). SI units have distinct advantages such as easier calculations and standards to remember. However, the US industry will not change to the metric system because of one reason alone COST. I was at conference on metriculation of units in the US the speaker said it cost the US industry billions of dollars to change over.


SI units do have an inherent ease of use but I remember being in school (Canada) hearing that we must always dimension our drawings in millimeters, for instance a room 13500 x 3600. The same instructors would howl in rage if the area of that room were given as 48600000 square millimeters.


Dimensioning in millimeters gives a false sense of accuracy that is not always there.


Butelja, I just saw your story. Best I`ve ever heard in my engineering career.


SI, US, Imperial. Who cares!
As long as we know clearly what we are measuring. The problem is not the units used but how it is used. E.g. regarding prefixes: It is quite clear what MMSCF/bbl is for a an engineer (Million, in the refinery business) but if your are in a part of the world were it is not that obvious (which units of measure is used) and reads e.g. MSCF/h. Is it 1000's or millions that is used? a simple attached abbreviation list with prefixes, units and acronymes covered helps a lot.

Same with measures like gallons, is it UK or US gallons that is meant?. Another example is when engineers use percent e.g. for measuring concentration, is it weight, volume or mole % or what?

The main point is that we should be clear on what units we are referring to and e.g. explicitly mention if we are talking US or UK gallons (and not just gallons). If not we are destined to make mistakes which can cost a fortune.If one can fulfil this requirement I dont think it matters so much which system thats is used, since it is "crystal" clear what is meant if done thoroughly.

Regarding changing units. That will only occur if there is an obviouos advantage of doing so. E.g. if one would like to have the same product (e.g. a car) irrespective if it is produced in US or elsewhere in the world, with the same units of measure built into the car. At that point the manufacturer will decide which system to be used and as long as it is clear for the suppliers and the customer which system is used, so whats the problem?

It is only to accept that different parts of the world will use different system.


Very interesting thread indeed.

I was fortunate enough to be born into a SI society, and thus "feel" in SI units. I have to agree with the defenders of the Imperial units: if one clearly specifies the units, no-one should feel uncomfortable.

In fact, how boring would life be if everyone spoke the same language? English is my second language, and I have lived a good life (so far) and certainly didn't make more mistakes in life (friendships etc.) as someone who speak the majority language of the world - probably Chinese. My point is, different units cannot change the science. In fact, the conversion from one set of units to another ceratinly increases the engineering "feel" and makes life interesting. It ceratinly also inspires different approaches to problems, which is a good thing.



For the sake of balancing readers' information, there is one site I found that considers butelja's funny story on railroad tracks a "rumor":


Rumor or not, I think butelja's message should be seriously considered.


The UK supposedly went metric in about '68 onwards as I recall. But we still use both units. We adapted because we had to. We are part of a much larger market and we needed to understand and not necessarily adopt other units.

I still work in Imperial and Metric. I'm 6'2" tall and weight 17 stone, my house is 500yds from the shops but I drive a 2litre turbo car.

I draw in mm and measure area in sq ft. I have a 32" TV set and buy drinks at the pub in pints. My car does 46MPG at a speed of 50MPH.

But when I go to France or Spain on holiday, I brush up on my schoolboy language training and communicate as best I can. I survive and its no big deal. The locals are generally very helpful and we haven't starved to death yet or ever not managed to buy our 60 litres of fuel.

Forces generated on pipe anchors are in kgF or KN. Pressure in PSI or Pa or Bar or kPA. I understand and use all of them fluently.  Most people (Luckily for us English), learn English and speak it quite often better than we can. They adjust and adapt to the needs of the time.

We as engineers have the ability to do the same. We shouldn't be frightened to understand or use it, and it is probably in a global interest to have common units.

I'm sure that one day....(a long long time fom now), there will be some sort of standardisation. But in the mean time, I'm still using feet and inches and kG and fahrenheit and centigrade and NM.

Friar Tuck of Sherwood


Friar Tuck,

You missed one out - Even though our cars do 46MPG at 50MPH, we buy petrol in litres. Also, although legally shops have to sell weighed goods in kilo's, we always ask for a pound of carrots or quarter of a pound of cheese etc...

We also still have a few people here who moan about decimalisation (which took place in february 1971) as if it is a bad thing not to have to work in pounds shillings and pence (12 old pence in a shilling?, 20 shillings in a pound? 240 old pence in a pound - and don't even start on guineas which were apparently a pound and a shilling).  Fortunatly I was born in 1972 so I missed out on all this.

In a similar manner (but less expensive than) the hubble telescope debacle, I spent a summer while at university working in an old cloth finishing machinery manufacturers in Salford (UK)where they managed to ruin a very expensive nylon roller they were turning because the drawing office of the company worked in metric and the machines downstairs on the shop floor were imperial.  The two departments were in the same building and they still got it wrong.  The D.O. expected the shop floor workers to convert every measurement prior to machining anything.


James Goodstadt



I know without hesitation that 1 mil is 39.37 thou.

1 mil is 1 thou. Don't ask me, 'mil' is a term your neighbours to the south use. How do they get from one thousandth of an inch to 'mil' in any rational step?

1 millimetre is 39.37 thou in England.

Mil is a slang term for millimetre over here in the UK. An American enginerr and I managed to tie ourselves in
knots over the difference in American and UK terminology.


If we learn from our mistakes,
I'm getting a great education!

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