RPM and horsepower are related factors in engine performance and ability. However, they are different types of units and you can cannot convert directly from one to the other. Though if you know the torque your engine is producing at a given RPM then it is possible to calculate the horsepower. The only way to measure torque is with a dynomometer, which is an expensive and very specialized device. If you do not know the torque specifications of your engine, consult a mechanic to see about measuring it with a dynomometer.
Determine the torque produced by your engine at a given RPM either from engine specifications or by having a mechanic measure it with a dynomometer.
Multiply your torque measurement, in foot-pounds, by the RPM.
Divide the result from Step 2 by 5252. This number is the horsepower output of your motor or engine.
