Quick calculations / Engines
Horsepower and Torque Calculator (hp, kW, PS, N·m, lb·ft)
Work out an engine's power from its torque and speed, or its torque from its power, in kilowatts, mechanical horsepower, and metric horsepower (PS), with torque in newton-metres or pound-feet.
Horsepower and Torque Calculator (hp, kW, PS, N·m, lb·ft): Power is torque × rotational speed: kW = N·m × rpm ÷ 9,549, and hp = lb·ft × rpm ÷ 5,252. 400 N·m at 4,000 rpm is 167.6 kW, which is 224.7 hp or 227.8 PS. 300 lb·ft at 5,252 rpm is exactly 300 hp. Runs 100% locally in your browser with zero server file uploads.
- Category
- Everyday tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs entirely in your browser
Power is torque times rotational speed. In imperial units, horsepower = torque in lb·ft × rpm ÷ 5,252, which is why torque and horsepower curves cross at 5,252 rpm; in metric, kW = torque in N·m × rpm ÷ 9,549. Mechanical horsepower (hp) is 745.7 W, while metric horsepower (PS, CV, or ch) is 735.5 W, about 1.4% less.
The constants
One horsepower is 33,000 ft·lbf per minute, and one revolution is 2π radians, so hp = torque × rpm ÷ (33,000 ÷ 2π) = ÷ 5,252.1. In SI units, kW = torque × rpm × 2π ÷ 60,000 = ÷ 9,549.3.
Unit conversions
To convert power or torque on its own, use kW to hp or N·m to lb·ft.
How to use it
- Choose power from torque or torque from power.
- Pick the units and enter the value and the engine speed in rpm.
- Read the result in every unit.
Privacy & limitations
Everything is calculated in your browser.
Related tools
Frequently asked questions
Why do torque and horsepower curves cross at 5,252 rpm?
Because 5,252 is 33,000 ÷ 2π, the constant in hp = lb·ft × rpm ÷ 5,252: at that speed the two numbers are equal on any engine measured in those units.
What is the difference between hp and PS?
Mechanical horsepower is 745.7 W; metric horsepower, written PS in Germany and CV or ch elsewhere, is 735.5 W, so the same engine has about 1.4% more PS than hp.
Should I use peak torque and peak power?
They usually come at different speeds; use the torque at the rpm you are interested in, from the engine's torque curve.
Free tool · runs in your browser · no account required