Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Where does "Mil" come from

Where does "Mil" come from

Where does "Mil" come from

As general office discussions go, this one is always one that I couldn't find the history on.

A mil is 0.001 inch.  Why is it called a mil?  Is it a millionth of some unit?  Is it of Latin or Greek origin?


RE: Where does "Mil" come from

And a millimeter is 1/1000th of a meter.  I suppose its not related to "million" but rather a latin or greek phrase relating to 1000.

RE: Where does "Mil" come from

I posted this in the Mechanical Engineers forum also.  It seems that "MIL(LE)" is Latin for thousand.

RE: Where does "Mil" come from

A MIL(lion) thanks.

RE: Where does "Mil" come from

here in Sweden we use the unit Mil, and thats the same as 10 kilometers

RE: Where does "Mil" come from

Hey, I know this thread is old, but I just discovered it.  


explains that mil is an alternate spelling of mill.

In 1791 the US congress established that there would be 10 mills in a cent, and 100 cents in a dollar.  So a mill was 1/1000 of a dollar.

Monetary usage is now obsolete, but a mil still represents a proportion equal to 1/1000 which is also equal to 25.4 microns.

Hope this satisfies your interest.

RE: Where does "Mil" come from

I'm not so sure that the monetary rate that Massey describes is obsolete.  My property tax rate is in mils/dollar value.

RE: Where does "Mil" come from

I don't know what your all talking about 0.001" is a thou and 0.0001" in a tenth - every engineer knows that!!

RE: Where does "Mil" come from

Millipede - a thousand footed bug

Millenium - a thousand years

Million (perhaps) - a thousand thousands?

Grazie mille - a thousand thanks

The possible incongruity of "million" aside, "milli" means thousand, or thousandth.

BTW, where I work, when I refer to a "mill" instead of "a thousandth (of an inch)", people look at me as if I have two heads.  This might be a peculiar "linguistic island", but my point is that mil is not universal.

RE: Where does "Mil" come from

one mil is .05625 degrees, or there are 6400 mils in 360 degrees.  Are they the sam mil and mill?  Where did the angular mil come from??

RE: Where does "Mil" come from

I have seen this unit expressed several times and I wish it was not used!  I practice in an area where imperial units and metric units are used.  A MIL has been used to express 'a thousandth of an inch' in imperial measure.  I have seen 'MIL' specified for products, etc. (e.g. poly vapor barier) on projects designed by and large using metric units.  Further, MIL is an acronym for other units of measure including angular measure (i.e. 1/6400 of a revolution) and volume measure (i.e. 1/1000 of a litre).

RE: Where does "Mil" come from

And M is the Roman numeral for one thousand.

It is quite common to see gas flow rates in Mcfd which is 1000 cubic feet/day, and MMcfd (one million cubic feet/day)

RE: Where does "Mil" come from

Just for the international flavor, "mil" is also Spanish for "thousand"

RE: Where does "Mil" come from

We use "mil" as an abbreviation (slang) for millimeters i.e. if we say it measures 50 mils - it means it measures 50mm.

RE: Where does "Mil" come from

I found this write up explaning for circular mils in 360 degrees.  


There are 2 pi radians or 6.28 radians in a circle or 6,280 thousands of a radian in a circle.  The army rounded it up to 6,400.  
The reason I remember for using mils was clarity and speed in communications.  Instead or telling someone to elevate their field pice 46 degrees-34 minutes you could say 827
 mills. Another one of those things where close is good enough ( like horse shoes, hand gernades and atom bombs)

RE: Where does "Mil" come from

Torch, be careful when new people come in. I think most US engineers and machinists would assume you meant "50 thou" if you said "50 mils"

RE: Where does "Mil" come from

A lot has been said about mil, thou, inches and millimeters here. But do you know how the relation 1 inch = 25,4 mm came about?

It is one of the first de facto standards that later was accepted as an official standard. Here is how and why:

Henry Ford needed accurate measurements and also standardised measurements in his mass fabrication of motor and other car parts. If he didn't have a standardised measure in all his factories, then the pieces wouldn't fit. Actually, mass production could not exist without standardised measures. So Henry Ford asked the Swedish inventor Carl Edward Johansson to deliver end-gauges (aka Joe-blocks) to Fords factories. Johansson was willing, but there was no fixed relation between inches and millimeters - the NBS was working on it and the Congress also had a say in this matter.

The Congress could not decide - there were a lot of different inches around and each congressman thougt that "his" inch was just right and all the others were more or less wrong, so there was no deciscion in the Congress - and no official relation between the inch and the millimeter in the NBS.

This went on for years, and Henry Ford got more and more irritated. At least he told Carl Edward Johansson to make the end-gauges to a convenient and rational measure and CEJ chose 25,4 mm to an inch and delivered the blocks. And ever after that an inch equals 25,4 mm.

CEJ had a reason to chose 25,4; it allowed to switch from metric to imperial threads in a lathe by using two wheels with 100 and 127 cogs on them. 25,0 mm had been too far off what was used in most states, but 25,4 was close enough to the majority of inches.

RE: Where does "Mil" come from

Correction: "at least" read "at last"

RE: Where does "Mil" come from

Thanks Binary.
I'll be careful if I'm ever in the US.
I live in New Zealand - ex South Africa. Both countries are pre-dominantly metric. (I say pre-dominantly because the old "obsolete" imperial system of measurement does still creep in in some areas.)
The abbreviation "mils" for millimeters is commonly used in both countries.

RE: Where does "Mil" come from

Dear skogsgurra,

Thanks for your valuable information.

There is a conflict with what I know.
According to the document titled "The Edison of Sweden : C.E. Johansson and the 'Standards of Standard'" written by Goeran Ahlstroem, C.E> Johansson contacted Henry Ford by letter, offering his collaboration.
Ref: http://www.ekh.lu.se/publ/lup/71.pdf

I am very much interested in Johansson's contribution in metrology.
Could you please let me know the reference where I can get more information on "inch-mm conversion history"? The thread of yours is the only information on inch-mm conversion history I have.

Thanks in advance.

RE: Where does "Mil" come from

Dear kanggadget,

Yes, you are right. CEJ contacted Henry Ford and offered his help. The development of the "standard inch" took about 30 years. Johansson had started to work on a unified inch in 1906 and there were several difficulties; different measuring temperatures and differing measures between Great Britain and the USA, evolving "practical standards". In 1912, Johansson decided to use the 25.4 mm inch at 20 centigrades and it was only in october 1932 that a committee in the Bureau of Standards decided to propose tha Johansson relation between inch and mm. The decision was taken by the ASA in March 1933.

My source is the Swedish book "C.E. Johansson 1864-1943, Master of measures" By Torsten Althin. Printed in Stockholm 1947.

There is a bibliography at the end of the book, which I could scan and mail you if you leav an e-mail address here.

Gunnar Englund

RE: Where does "Mil" come from

Dear Gunnar Englund (skogsgurra),

Thank you very much for your reply.
I am afraid that perhaps all references are written in Swedish language. However, I would be very happy to recieve the bibliography of the book from you.
My email address is : cskang@kriss.re.kr
(I am working in a metrology institute in Korea.)

Thank you very much again for your hospitality.

Chu-Shik Kang.

RE: Where does "Mil" come from

These are the kind of stories that made India go metric all the way. I guess many other countries and people have not made up their mind yet. It's matter of educating people and come to an agreement in retaining the most useful terminology and dropping the confusing terminology. By widening the scope of SI units and standardization we can make this world an easier place to accomplish our day to day tasks.

For example look at the presuure units that are in psi, psig, psia, "H2O, "Hg, mmHg, cmHg, ft of H2O, Torr, milliTorr, kPa, Pa, bar, millibar, lbf/in2, kips, kgf/cm2, and so on.

Why US is not committed to make progress in this very important area, like they tried to do for the milleneum bug Y2K which proved not to be as big a scare as they had claimed it to be? People worlwide are definitely loseing time and money going through a number of unnecessary calculation on a daily basis, that could be avoided.

RE: Where does "Mil" come from

I dunno, criticizing the U.S. for its failures is fashionable nowadays but life here is so fun and so much freedom!  I left the Asian country I grew up in because I could be thrown in jail if I criticize.  Maybe it's the reason I immigrated here and never looked back.  So let's all lighten up and discover the joys of knowing inches/feet/ounce/gram/horsepower/etc.  Screw metric, it's too impersonal. (toungue-in-cheek)

RE: Where does "Mil" come from

I'll stay out of the political dabate (but I'll just add that I'm in the U.S. and I do favor the metric system).

Responding to torch - sounds like the term "mil" is used differently in the metric world as you pointed out to millimeters.  Here in the U.S., if I say "The sheet of paper I'm writing on is 4 mils thick" it means 0.004 inches.

jim s.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close