WheelSignal

WheelSignal

Results printed from https://wheelsignal.com/horsepower-torque-calculator. Nominal estimates; see assumptions below.

Horsepower & torque calculator

Turn torque and RPM into power, or power and RPM into torque, in whichever units you use.

Power and torque

Calculate
Values
Unit: RPM

Unit choices are saved only if you tick the box, in this browser’s local storage. Measurements are never saved or sent anywhere. A shared link carries the inputs after the # in the address, which browsers don’t send to the server.

Results

Choose what to calculate, enter the values, or press Try an example, then Calculate.

How to use the horsepower and torque calculator

  1. Choose whether you have torque and want power, or have power and want torque.
  2. Enter the value and its unit, and the engine speed at which it was measured.
  3. Press Calculate to see the result in every common unit.

Power and torque must come from the same RPM. Peak power and peak torque usually occur at different engine speeds, so a peak-torque figure and a peak-power RPM can’t be combined.

Worked example

300 N·m at 5,000 RPM: power = 300 × 2π × 5,000 ÷ 60 = 157,080 W, which is 157.1 kW, 210.6 hp or 213.6 PS.

Units

Exact definitions used
UnitDefinition
1 hp (mechanical)550 ft·lbf/s = 745.699872 W
1 PS (metric hp)75 kgf·m/s = 735.49875 W
1 kW1,000 W
1 lb·ft1.355818 N·m

Formulas used

power (W) = torque (N·m) × 2π × RPM ÷ 60 torque = power (W) × 60 ÷ (2π × RPM) hp = torque (lb·ft) × RPM ÷ 5252.113 (5,252.113 = 33,000 ÷ 2π)

Frequently asked questions

Why do horsepower and torque curves cross at 5,252 RPM?

Because of the units. Horsepower = lb·ft × RPM ÷ 5,252.1, so at 5,252 RPM the two numbers are equal. In metric units (kW and N·m) there’s no such crossing point; it’s an artefact of mixing feet, pounds and the horsepower definition.

What’s the difference between hp, PS and kW?

Mechanical horsepower (hp, sometimes bhp) is 745.7 W. Metric horsepower (PS, CV or ch) is 735.5 W, about 1.4% smaller. Kilowatts are the SI unit used in most official specifications. 100 kW is 134.1 hp or 136.0 PS.

Can I calculate wheel horsepower from engine horsepower?

Not reliably with a fixed percentage. Drivetrain losses depend on the gearbox, differential, tires, temperature and how the dynamometer measures. This calculator converts power and torque at the same point in the drivetrain.

Is torque at the wheels the same as engine torque?

No. Gearing multiplies torque and divides speed: in a gear with an overall ratio of 10:1, wheel torque is roughly ten times engine torque (less losses) while wheel speed is a tenth of engine speed. Power stays the same apart from losses.

Last updated .