Convert torque and speed into power. Enter the torque in lb-ft or newton-meters and the RPM, and see horsepower, kilowatts and metric horsepower. Free, private, and runs entirely in your browser.
Power is torque multiplied by rotational speed. With torque in pound-feet and speed in RPM, dividing by 5,252 gives horsepower. In metric units, kilowatts equal torque in newton-meters times RPM divided by 9,549.
Why 5,252? It comes from the definition of horsepower as 33,000 ft-lb per minute divided by 2π, since one revolution is 2π radians.
Where do the torque and horsepower curves cross? At 5,252 RPM, torque in lb-ft and horsepower are numerically equal.
An engine makes 300 lb-ft at 5,000 RPM. Horsepower = 300 × 5,000 ÷ 5,252 ≈ 285.6 hp, which is about 213 kW.
What is the difference between hp and PS? Metric horsepower (PS) is about 1.4% larger than mechanical horsepower.
Can I find torque from horsepower? Yes. Torque in lb-ft equals HP × 5,252 ÷ RPM.
James Watt introduced the horsepower in the 1780s to compare his steam engines with the draft horses they replaced. The mechanical horsepower is standardized as 33,000 foot-pounds per minute, which leads to the constant 5,252 when torque and speed are used. The relation explains why torque and power curves cross at 5,252 RPM on a dyno chart.
Use this calculator to compare engines and motors, or to turn dyno readings into power. A 400 N·m motor at 3,000 RPM delivers about 125.7 kW. For gear sets, use the gear ratio calculator.
How do I convert kW to hp? Multiply kilowatts by 1.341 to get mechanical horsepower.
How do I convert hp to torque? Torque (lb-ft) = HP × 5,252 ÷ RPM.