Klauss is right. True total in phase power is what really matters here, but then you have to estimate the efficiency to come up with developed mechanical power.
That is difficult, but you might be able to make a VERY rough estimate of mechanical efficiency by measuring the slip speed as a percentage, and doubling that.
Check out the rating plate data.
There should be an operating RPM which when the number of poles and excitation frequency are taken into account, will tell you the percentage slip. Typically for example you might find 6% slip for an 88% efficient motor. (100-(2x6%)=88%
That's not always true, but it should get you close as a rule of thumb.
Full load amps will be in VA not Watts, and sometimes there is a power factor quoted, it all gets a bit tricky using that.
Only way to know for sure is with a tachometer, torque sensor, and true power meter.