Horsepower, Torque & kW
Power from torque and rpm, or torque from power, in hp, PS, kW, lbf·ft and N·m with exact NIST factors — the 5,252 relation worked in the open.
The matching power and torque at your rpm in every customary unit, from either one, with the conversion factors stated.
Example: 400 N·m at 3,000 rpm is 125.7 kW = 168.5 hp = 170.9 PS; 300 lbf·ft at 5,252 rpm is exactly 300 hp.
Torque times speed,
and a constant.
Why power and torque are one quantity at a given rpm, where 5,252 comes from, the exact unit factors, and which rating standard your number carries.
Power is torque times angular speed
Power = torque × angular velocity. With torque in newton-metres and speed in rpm, P (W) = T × rpm × 2π ÷ 60. In customary units, one horsepower is 33,000 ft·lbf per minute, so hp = T (lbf·ft) × rpm ÷ 5,252.1 — the constant is 33,000 ÷ 2π. It follows that torque and power curves in lbf·ft and hp cross at 5,252 rpm, always.
Units
Mechanical horsepower (550 ft·lbf/s) is exactly 745.6999 W and metric horsepower (PS, CV, ch) is 735.4988 W; one pound-force foot is 1.355818 N·m — the factors are NIST SP 811’s. A kW figure is the SI one; bhp on a British sheet means brake (measured) horsepower, usually mechanical.
Crank, wheel and the rating standard
Torque and power here are a pair at one rpm on the same shaft. A figure measured at the wheels includes drivetrain loss and is lower than at the crank; converting between them needs the loss, which this page does not assume. Ratings also follow a standard — SAE J1349, DIN 70020 and ECE R85 differ in accessories, correction and where they measure — so quote the one on the sheet.
What the number does not settle
Nothing here predicts the power of an engine from its size or specification; it converts between figures you already have. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
Last reviewed 18 September 2026. How results are checked: How we verify.