Horsepower Calculator
Calculate horsepower from torque and RPM with the classic hp = torque × RPM ÷ 5252 formula.
How it works
Horsepower = torque (lb-ft) × RPM ÷ 5252
Horsepower is the rate of doing work, so it combines twisting force (torque) with how fast the engine spins (RPM). The constant 5252 comes from the definition of one horsepower (33,000 lb-ft per minute) divided by 2π. A direct consequence: below 5,252 RPM torque is the larger number, above it horsepower is larger, and at exactly 5,252 RPM they are equal — which is why every dyno graph shows the two lines crossing there.
Worked example
400 lb-ft at 5,252 RPM makes exactly 400 hp (about 298.3 kW). The same 400 lb-ft at 3,000 RPM makes only about 228 hp, because horsepower rises with engine speed.
Frequently asked questions
Why is the number 5252 in the formula?
One horsepower is 33,000 foot-pounds of work per minute. Converting torque (lb-ft) and RPM into that unit divides out to 33,000 ÷ 2π ≈ 5,252, the constant that ties the two together.
Do horsepower and torque curves always cross at 5,252?
Yes, on any dyno plotted in lb-ft and hp. It is a mathematical certainty of the formula, not a property of a particular engine, so the crossover point is always 5,252 RPM.
Is horsepower or torque more important?
Torque is the force you feel pushing you back; horsepower is torque sustained at speed and largely sets top speed. Both matter — strong low-end torque feels quick, while high-RPM horsepower keeps pulling.
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This calculator is for educational purposes. Double-check important results before acting on them.