How is horsepower ratings determined in a motor?

Answer 1

When you see a horsepower rating for an engine, it will also list the torque at a specific rpm.

Power = Torque x Angular Velocity. Units are (ft-lbs) x (1/sec). Divide by 550 ft-lbs/sec and you get horsepower.

(Be sure to convert rpm’s to radians/sec)

Hope that helps!