Calculate mechanical horsepower from torque and RPM, convert between HP, kW, and PS, or compute power from force and velocity for engines and motors.
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Horsepower (HP) is the standard unit for measuring engine and motor power output. Our calculator helps you compute horsepower from torque and RPM, calculate power from force and velocity, or convert instantly between HP, kW, PS (metric horsepower) and watts for any mechanical system.
Horsepower was developed by James Watt to compare steam engine power to draft horses. One mechanical horsepower equals 550 foot-pounds per second or 33,000 foot-pounds per minute. Today, different horsepower standards exist including Imperial (HP), Metric (PS/CV), and Electrical (exactly 746W).
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The constant 5252 comes from (33,000 ft·lb/min) ÷ (2π rad/rev). Since HP = 33,000 ft·lb/min and torque is measured in lb·ft with RPM in revolutions per minute, this constant converts the units correctly.
Imperial Horsepower (HP) equals 745.7 watts and is based on 550 ft·lb/s. Metric Horsepower (PS/CV/pk) equals 735.5 watts and is based on 75 kgf·m/s. PS is about 1.4% less than HP.
Divide kilowatts by 0.7457 to get Imperial HP, or divide by 0.7355 to get Metric HP (PS). For example, 100 kW ≈ 134 HP ≈ 136 PS.
Brake horsepower is power measured at the engine crankshaft, before transmission losses. Wheel horsepower (WHP) is lower due to drivetrain friction, typically 15-20% less than BHP.
Multiply Imperial horsepower by 0.7457 to get kilowatts (multiply metric PS by 0.7355). For example, 150 HP × 0.7457 ≈ 111.9 kW. To go the other way, divide kW by 0.7457.