Not really. You could measure and make an educated guess, but it would not tell you the limits from a protection standpoint. Still, if you UNDERestimate it, the risk becomes mainly nuisance tripping.
Eng-Tips: Help for your job, not for your homework Read faq731-376
If the unit is built to standard. Shaft measurement will do, mounting dimension you'll then find the FRAME # but it's just an approximation.
Better to run the machine and test it as itsmoked said.