Horsepower from Torque Calculator
Horsepower and torque are related through engine speed. Torque measures twisting force; horsepower measures the rate at which that force does work. Given torque in pound-feet and engine speed in RPM, horsepower follows from the standard formula: torque times RPM divided by 5,252. This calculator computes horsepower from torque and RPM and also shows the power in kilowatts. Enter the torque and engine speed to see the result.
Horsepower formula
horsepower = (torque in lb-ft * RPM) / 5,252
kilowatts = horsepower * 0.745699872
The constant 5,252 comes from one horsepower being 33,000 foot-pounds per minute divided by 2 times pi radians per revolution. The kilowatt result uses the exact mechanical-horsepower to watt conversion.
Worked example
An engine producing 300 lb-ft of torque at 5,252 RPM makes (300 times 5,252) / 5,252 = 300.00 horsepower. This shows the crossover point: at exactly 5,252 RPM, horsepower equals torque numerically. In kilowatts, 300 hp times 0.745699872 = 223.71 kW.
Horsepower from torque: frequently asked questions
How do you calculate horsepower from torque and RPM?
In US customary units, horsepower equals torque in pound-feet multiplied by engine speed in revolutions per minute, divided by 5,252. The formula is HP = (torque times RPM) / 5,252. This relationship comes from the definition of one mechanical horsepower as 33,000 foot-pounds of work per minute, combined with the 2 times pi radians in one revolution.
Where does the constant 5,252 come from?
One mechanical horsepower is defined as 33,000 foot-pounds per minute. Power equals torque times angular speed, and angular speed in radians per minute is RPM times 2 times pi. Dividing 33,000 by 2 times pi gives approximately 5,252. So horsepower = torque times RPM divided by 5,252. This is also why horsepower and torque curves always cross at 5,252 RPM on a dynamometer chart.
Why do horsepower and torque curves cross at 5,252 RPM?
Because horsepower is torque times RPM divided by 5,252, the two quantities are numerically equal exactly when RPM equals 5,252. At that engine speed the multiplier (RPM / 5,252) equals one, so horsepower equals torque. Below 5,252 RPM torque exceeds horsepower numerically, and above it horsepower exceeds torque.
Does this formula work for metric units?
This calculator uses US customary units: torque in pound-feet and the constant 5,252 to give mechanical horsepower. In metric systems, power is usually expressed in kilowatts, where power in watts equals torque in newton-metres times angular speed in radians per second. To use the 5,252 formula, keep torque in pound-feet and speed in RPM.
Official sources
- National Institute of Standards and Technology: Guide for the Use of the International System of Units (SI), power conversions.
- U.S. Environmental Protection Agency: EPA vehicle and engine certification.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.