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.