It varies from individual printer to individual printer, as parts for printers vary a little bit in tolerances.
Easy one, if you got calipers to measure distance accurately. Digital calipers are pretty cheap now, although they are not really more accurate than traditional calipers.
Trim the filament flat, then tell it to manually extrude 100mm of filament.
Cut again using same cutting technique, and measure the filament flat to tell what it the length really is, that tells you what it's currently doing, and you can adjust the steps per mm accordingly.
It's worth getting a set of accurate calipers, for adjusting steps per mm of X, Y and Z, to get models printing to 0.1mm accuracy (or better).
Edited 3 time(s). Last edit at 11/01/2016 12:09PM by DragonFire.