Power Comparison Between Electric and GasolinePowered ...
The HP rating of a motor or an engine is given at its rated speed. The rated speed is around 1,750 RPM for an electric motor and 3,800 RPM for an engine. Since HP = Torque x Speed x 32,572 (where Torque is given in lbsft) then for a 3,800 RPM 20 HP engine run at 1,750 RPM (equal to a motor speed), it will provide only around HP) so at this speed, a 10 HP motor is sufficient.