How to determine amp rating ?

[Tat2]

So, if I understand you correctly, to determine a motor's potential amp draw you'd just divide watts by volts? watts/volts = amps? Or am I misunderstanding you, or missing something here? I understand that these are very rough estimations, and there's a lot that goes into what kind of draw a brushless system will place on the batteries during real world use, but is it just that simple?
The guy who asked me about this basically just wants to know how to determine what a motors amp rating is, or the amp range (continuous to peak) that the OEM has determined for a particular motor, where the OEM hasn't included that info, so that he won't purchase a motor which is ill suited to his needs. So it's watts/volts = amps?