Horsepower Calculator
Calculate horsepower from torque and engine RPM, or torque from horsepower and RPM. In metric units these two modes work in N·m and kW instead. Two more modes convert between kW and HP and find power from a force and a velocity. For quarter-mile ET and trap speed, use the Engine Horsepower Calculator.
How to use the Horsepower Calculator
- Choose US / Imperial or Metric units, then pick a mode: torque to horsepower, horsepower to torque, kW and HP, or mechanical power.
- Enter the two values the mode asks for. The kW and HP mode takes one value and a direction.
- Press the Calculate button. You get the result and the formula with your numbers in it.
- Switching units or modes clears the result, so press Calculate again after you switch.
The horsepower formulas
HP = (Torque × RPM) / 5252 · · · kW = (N·m × RPM) / 9549.3 · · · HP = (Force × Velocity) / 550 · · · kW = HP × 0.7457
In US units torque is in lb-ft, force in lbf and velocity in ft/s. In metric units torque is in N·m, force in newtons, velocity in m/s and power in kW. RPM is revolutions per minute in both. The 5,252 constant comes from converting work and time units.
Worked example
A car making 350 lb-ft of torque at 4,500 RPM has (350 × 4,500) / 5,252 = 299.89 hp, the figure the calculator shows. Turned around, 300 hp at 4,500 RPM needs 300 × 5,252 / 4,500 = 350.13 lb-ft of torque.
Frequently asked questions
Why does horsepower = torque at 5,252 RPM?
Because 5,252 is the constant in the formula. At 5,252 RPM the horsepower and the lb-ft are the same number, so a dyno graph in those units shows the two curves crossing there.
What's the difference between HP and brake HP?
Brake horsepower (bhp) is measured at the crankshaft. Wheel horsepower is measured at the drive wheels and comes out lower, because the gearbox and drive line use up some of the power on the way.
Is horsepower the same as torque?
No. Torque is a turning force and horsepower is the rate of doing work. Horsepower is torque times RPM divided by 5,252, so the same torque gives more horsepower at a higher RPM.
Can this calculator estimate horsepower from a quarter-mile run?
No. This page works from torque and RPM, from kW, or from force and velocity. The Engine Horsepower Calculator estimates horsepower from weight with an elapsed time or trap speed, and quarter-mile ET and trap speed from horsepower and weight.