🐎 Horsepower Calculator
Horsepower is torque multiplied by speed: the same twisting force makes more power the faster the engine spins. The constant 5252 comes from James Watt's definition of horsepower (33,000 ft-lb per minute divided by 2π).
Enter the torque and RPM at the same engine speed — mixing peak torque RPM with redline RPM gives a meaningless number.
How to use this calculator
Enter an engine's torque in pound-feet and the RPM it was measured at to get horsepower from the classic formula.
- Enter the Torque in lb-ft.
- Enter the Engine speed in RPM, measured at the same point as the torque.
- The horsepower appears instantly.
- Read the kilowatt equivalent too.
Frequently asked questions
What formula does the Horsepower Calculator use?
Horsepower equals torque times RPM divided by 5252. The constant comes from James Watt's definition: 33,000 foot-pounds per minute divided by 2 pi.
Can you give a worked example?
300 lb-ft at 4000 RPM gives 228.48 horsepower, which is 170.38 kilowatts.
Why must torque and RPM come from the same point?
Horsepower is torque times rotational speed at one instant. Mixing peak torque RPM with redline RPM combines two different moments and the result is meaningless.
What is the kilowatt figure for?
Kilowatts are the metric power unit used in most of the world. One horsepower equals 0.7457 kilowatts.