Horsepower from Torque Calculator
Calculate horsepower from engine torque and RPM using the standard formula HP = Torque × RPM ÷ 5252.
How to use this tool
- Enter the engine torque in pound-feet (from a dyno or spec sheet).
- Enter the RPM at which that torque figure is measured.
- The calculator applies HP = Torque × RPM ÷ 5,252 and returns horsepower.
Use the dyno formula to convert engine torque and RPM into horsepower.
Formula
Horsepower = Torque (lb·ft) × RPM ÷ 5,252
The constant 5,252 derives from the definition of horsepower: 1 HP = 33,000 ft·lbf/min, giving 2π × 33,000 ÷ 60 ≈ 5,252 when using shaft revolution rates.
How it works
This calculator applies the standard mechanical engineering relationship between torque, rotational speed, and power to convert engine output measured in pound-feet and RPM into horsepower.
The formula is exact under the SAE definition of horsepower and is the same equation used by engine dynamometers to derive HP from measured torque curves. It assumes torque is in pound-feet and RPM is in revolutions per minute; results in other unit systems (e.g., kilowatts from Newton-metres) require different constants.
Worked example
Worked example
- Torque = 300 lb·ft; engine speed = 5,252 RPM.
- Multiply torque by RPM: 300 × 5,252 = 1,575,600.
- Divide by the constant 5,252: 1,575,600 ÷ 5,252 = 300 HP.
Horsepower = 300 HP.
Key terms
- Torque
- A rotational force measured in pound-feet (lb·ft) or Newton-metres (N·m); the twisting effort an engine produces at the crankshaft.
- RPM (revolutions per minute)
- The number of complete crankshaft rotations per minute; a measure of engine speed.
- Horsepower (HP)
- A unit of power equal to 550 foot-pounds per second or 33,000 foot-pounds per minute, defined by James Watt in the 18th century.
- 5,252 constant
- The value at which torque (lb·ft) numerically equals horsepower at any given RPM; it comes from dividing 33,000 ft·lbf/min by 2π and multiplying by 60.
- Dynamometer (dyno)
- A device that measures an engine's torque and RPM output, from which horsepower is calculated using this same formula.
Frequently asked questions
- What is the formula for horsepower from torque?
- HP = Torque (lb·ft) × RPM ÷ 5,252. The constant 5,252 comes from unit conversion: one horsepower equals 33,000 ft·lb/min, and 33,000 ÷ (2π) ≈ 5,252.
- Why do HP and torque curves cross at 5,252 RPM?
- Because at exactly 5,252 RPM the divisor equals the multiplier, so HP = Torque numerically. On a dyno chart the two curves always intersect at that engine speed.