Horsepower from Torque Calculator
Convert torque and RPM into horsepower with the classic hp = torque × RPM ÷ 5252 formula.
How it works
Horsepower = torque (lb-ft) × RPM ÷ 5252
Horsepower is the rate at which torque does work, so it multiplies the twisting force by how fast the crank is spinning. The magic constant 5,252 comes from the definition of one horsepower — 33,000 lb-ft of work per minute — divided by 2π radians per revolution. Because of it, the same torque makes more horsepower the higher the RPM, and below 5,252 RPM the torque figure is always the larger of the two numbers.
Worked example
A motor making 300 lb-ft right at 5,252 RPM produces exactly 300 hp (about 223.7 kW). Hold that same 300 lb-ft down at 3,000 RPM and it is only about 171 hp, because power scales with engine speed.
Frequently asked questions
Why is 5252 in the horsepower formula?
One horsepower equals 33,000 foot-pounds of work per minute. Dividing that by 2π (the radians in one revolution) gives 5,252 — the constant that links torque in lb-ft and speed in RPM to horsepower.
Do the torque and horsepower curves always meet at 5252?
Yes, on any dyno graph plotted in lb-ft and hp. It is a property of the formula, not the engine, so the crossover is always at 5,252 RPM regardless of the motor.
How do I convert horsepower to kilowatts?
Multiply horsepower by 0.7457. So 300 hp is about 223.7 kW. Metric horsepower (PS), common on European spec sheets, is slightly smaller — divide the kW figure by 0.7355.
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Educational estimate. Real-world results vary with conditions, tuning and measurement.