Horsepower Calculator
Convert hp, PS, kW and work out power from torque and rpm.
About this tool
Enter a power figure in any unit to see it in all the others, then enter torque and engine speed to get power, or see how much torque a power figure needs at a given rpm.
Power, torque and rpm
Mechanical horsepower (hp or bhp, used in the UK and US) is 745.7 watts. Metric horsepower (PS in Germany, CV in France and Italy, pk in the Netherlands) is slightly smaller at 735.5 W, so a 150 PS car makes about 148 hp or 110 kW. Electrical horsepower, used for motors, is exactly 746 W. Power is torque multiplied by rotational speed. In everyday units that becomes hp = lb-ft × rpm ÷ 5,252 or kW = N·m × rpm ÷ 9,549, so an engine making 300 N·m at 4,000 rpm is producing about 126 kW (169 hp) at that speed. That constant is why hp and lb-ft curves always cross at 5,252 rpm. Honest limits: peak power and peak torque usually occur at different rpm, so the headline numbers can't be multiplied together, and power measured at the wheels on a dyno is typically 10–20% below the crankshaft figure. The unit converter and the fuel cost calculator are related.
Frequently asked questions
How many hp is 1 kW?
1 kW is about 1.34 mechanical horsepower; 1 hp is 0.746 kW.
What is the difference between hp and PS?
PS (metric horsepower) is 735.5 W and hp (mechanical) is 745.7 W, so 100 PS is about 98.6 hp.
How do I calculate horsepower from torque?
Multiply torque in lb-ft by rpm and divide by 5,252; for kW, multiply N·m by rpm and divide by 9,549.
Why do torque and horsepower cross at 5,252 rpm?
Because hp = lb-ft × rpm ÷ 5,252, the two numbers are equal at exactly that speed.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.