Why is 5252 the constant in the formula?

5252 comes from converting rotational work into horsepower: one horsepower is 33,000 ft-lbs per minute, and dividing by 2π gives 5252. It is also the RPM at which horsepower and torque curves always cross.

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Power

Torque to HP Calculator

Convert engine torque and RPM into horsepower and kilowatts with the classic HP = torque × RPM ÷ 5252 formula.

Power output

285.6 HP

Kilowatts—

Torque (ft-lbs)—

Torque (Nm)—

Horsepower across the rev range

HP at your torque figure held flat, for a spread of engine speeds.

How it works

Horsepower is the rate of doing work, it combines how hard the engine twists (torque) with how fast it spins (RPM). The constant 5252 converts the units so that torque in foot-pounds and speed in RPM give power in horsepower.

HP = torque (ft-lbs) × RPM ÷ 5252
kW = HP × 0.7457

Worked example

An engine making 300 ft-lbs at 5000 RPM produces 300 × 5000 ÷ 5252 = 285.6 HP (about 213 kW).

Frequently asked questions

How do you convert torque to horsepower?

HP = torque (ft-lbs) × RPM ÷ 5252. Convert Nm to ft-lbs first if needed.

Why 5252?

It comes from the definition of horsepower and 2π; it is also the RPM where the HP and torque curves always intersect.