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Horsepower Calculator: Torque × RPM ÷ 5252

Pick what you want to find, then enter the other two quantities. The calculator uses power equals torque times angular speed, shows the familiar 5252 shortcut and converts the result to horsepower, metric horsepower, kilowatts and watts.

By Adzita Editorial Team · Updated 2026-11-03 · How we build and check our tools

Power, torque and speed

Mechanical power is torque multiplied by angular speed. In SI units, P (watts) = T (N·m) × 2π × rpm ÷ 60. Converting to imperial units, with torque in pound-feet and speed in revolutions per minute, one horsepower is defined as 33,000 foot-pounds per minute, so hp = T × rpm × 2π ÷ 33,000. The constant 33,000 ÷ 2π equals about 5,252.11, which is where the well-known shortcut hp = T × rpm ÷ 5252 comes from.

One consequence is that the horsepower and torque curves of any engine cross at 5,252 rpm when both are plotted in these units. Below that speed horsepower is less than torque in number, above it more.

Horsepower, PS and kilowatts

The two horsepower units differ by about 1.4 percent, which can matter when comparing specification sheets from different regions. Many manufacturers list power in kilowatts alone. To go from kilowatts to mechanical horsepower, multiply by about 1.341. This tool uses mechanical horsepower for the headline figure and shows PS beside it.

What kind of horsepower is it?

• Crank or brake horsepower. Measured at the engine output shaft, often on an engine dynamometer.
• Wheel horsepower. Measured at the drive wheels on a chassis dynamometer, lower than crank figures because of losses in the gearbox, differential and tires.
• Rated and nameplate power. For electric motors it is the shaft output at rated load, not the electrical input.

The calculator does not know which of these you are measuring. It simply converts between the three variables, so be consistent about where the torque and speed were measured.

Limits and safety

This tool is for estimating and learning. It does not model gear ratios, drivetrain losses, altitude, temperature or fuel. Motor, pump, vehicle and lifting equipment must be sized and operated within the maker's limits and the applicable codes, and a qualified engineer or technician must decide ratings for real machinery. Rotating equipment can injure or kill, so never remove guards or exceed rated speeds based on a calculated value alone.

Remember also that a single peak horsepower number says little about how an engine or motor behaves in use. Torque at the speeds where the machine actually works, the shape of the power curve, cooling, duty cycle and gearing all decide whether a drive is suitable. Electric motors are normally rated for continuous output, while engines are often quoted at their peak, so compare like with like before drawing conclusions from two data sheets.

Worked example

An engine producing 300 lb·ft of torque at 5,000 rpm.

Inputs

Result

Estimating note: Quantities and ratings here are estimates for planning and learning. Products, local codes and site conditions differ, so check manufacturer data and local regulations, and use a qualified professional for electrical, structural or safety-critical work.

Frequently asked questions

Related calculators

References and sources

1. NIST Guide for the Use of the International System of Units (SI): power and torque units and conversions. Link

Check primary sources for anything you rely on.