Owais,
Typically "tray rating" refers to hydraulic calculations using vapor and liquid rates (plus props such as density, viscosity, surface tension) which are most often obtained from process simulation. These ratings are intended to calculate % of jet flood (vapor rate) or downcomer backup flooding (liquid rate) using some pretty well established correlations. If this is your intent (hydraulic rating) please let us know and I am sure you will get much help.
Tray efficiency is a bit more complicated topic, beginning with the definition of efficiency. It appears you may wish to calculate an overall column efficiency using operating data, I have several times given a procedure to do this- most recently thread124-140090.
If you wish to estimate tray efficiency in advance (i.e. design) then there are several methods ranging from rules of thumb to rigorous mass transfer methods based on point efficiency (using slope of equilibrium curve and L/V ratio)- such calculations are described in Perry's Handbook and Kister's Distillation Design. If this is your interest then please give a little more details of your problem and you may get some help on that as well.
Best wishes for now,
sshep
