Why is 5,252 in the formula?

One horsepower is defined as 33,000 foot-pounds of work per minute. Converting rotational work to that unit introduces a factor of 2π, and 33,000 divided by 2π is about 5,252, which is why torque in lb-ft times RPM divided by 5,252 gives horsepower.

Why do torque and horsepower curves cross at 5,252 RPM?

Because HP = torque × RPM ÷ 5,252, the two values are numerically equal exactly when RPM is 5,252. On a dyno chart the horsepower and torque lines always intersect at that engine speed.

What inputs and outputs does this calculator use?

It takes torque in pound-feet and speed in RPM, and returns power in horsepower, watts, and kilowatts. It does not convert from quarter-mile times or vehicle weight, which is a separate estimation method.

How do I convert horsepower to kilowatts?

Multiply mechanical horsepower by 745.7 to get watts, then divide by 1,000 for kilowatts. So 300 HP is about 223.71 kW, the figure this calculator reports alongside the watts value.

Horsepower Calculator

Torque

lb-ft

RPM

Horsepower300.00 HP

Watts223,710

Kilowatts223.71

This horsepower calculator finds an engine's power output from its torque and rotational speed using the classic relationship between work and time. Torque measures twisting force while RPM measures how fast the shaft spins, and together they define how much power the engine delivers. The result is shown in mechanical horsepower along with the equivalent in watts and kilowatts, so you can compare ratings across imperial and metric specifications.

Formula

HP = (Torque × RPM) ÷ 5252

Torque: Rotational force in pound-feet (lb-ft)
RPM: Rotational speed in revolutions per minute
5252: Constant from 33,000 ft-lb/min per HP divided by 2π
HP: Mechanical horsepower output

How it works

Enter the engine torque in pound-feet (lb-ft) and the rotational speed in revolutions per minute (RPM).
The calculator multiplies torque by RPM and divides by 5,252, the constant that links lb-ft and RPM to horsepower.
It reports horsepower and converts it to watts and kilowatts using 1 HP = 745.7 watts.

Worked example

An engine producing 300 lb-ft of torque at 5,252 RPM.

Multiply torque by RPM: 300 × 5252 = 1,575,600.
Divide by 5,252: 1,575,600 ÷ 5252 = 300 HP.
Convert to kilowatts: 300 × 745.7 ÷ 1000 = 223.71 kW.

The engine makes 300 HP, equal to about 223,710 watts (223.71 kW).

Frequently asked questions

Why is 5,252 in the formula?: One horsepower is defined as 33,000 foot-pounds of work per minute. Converting rotational work to that unit introduces a factor of 2π, and 33,000 divided by 2π is about 5,252, which is why torque in lb-ft times RPM divided by 5,252 gives horsepower.
Why do torque and horsepower curves cross at 5,252 RPM?: Because HP = torque × RPM ÷ 5,252, the two values are numerically equal exactly when RPM is 5,252. On a dyno chart the horsepower and torque lines always intersect at that engine speed.
What inputs and outputs does this calculator use?: It takes torque in pound-feet and speed in RPM, and returns power in horsepower, watts, and kilowatts. It does not convert from quarter-mile times or vehicle weight, which is a separate estimation method.
How do I convert horsepower to kilowatts?: Multiply mechanical horsepower by 745.7 to get watts, then divide by 1,000 for kilowatts. So 300 HP is about 223.71 kW, the figure this calculator reports alongside the watts value.

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