Horsepower Calculator

Estimate mechanical horsepower from torque and RPM or convert kilowatts to horsepower

Torque is in lb-ft. Mechanical hp = torque × RPM ÷ 5252.

Your result will appear here.

About the Horsepower Calculator

Horsepower is a unit of power used for engines, motors and mechanical equipment. The calculator converts between horsepower and other power units or derives horsepower from torque and rotational speed when those values are known.

Rated engine horsepower and power delivered at the wheels are not the same measurement. Drivetrain losses, test standards and operating speed all affect which number is being discussed.

How to Use the Horsepower Calculator

  1. Choose whether you are converting a power unit or calculating horsepower from torque and RPM.
  2. Enter torque using the unit expected by the calculator and enter rotational speed.
  3. Calculate horsepower or the equivalent kilowatt value.
  4. Keep engine, shaft and wheel-power measurements clearly labeled when comparing specifications.

How the Calculation Works

Mechanical power is torque multiplied by angular speed. In U.S. customary units, horsepower is commonly calculated as HP = torque(lb-ft) × RPM ÷ 5252.

Metric power can be calculated in watts from torque in newton-metres and angular speed in radians per second, then converted to kilowatts or horsepower.

Worked example

Horsepower Calculator Worked Example

300 lb-ft at 4,000 RPM

Horsepower = 300×4,000 ÷ 5,252 ≈ 228.5 hp. This represents the power corresponding to that torque at that rotational speed.

Result guide

Understanding Your Horsepower Calculator Result

Torque and horsepower describe different aspects of engine output. Horsepower rises with rotational speed for the same torque because power is the rate of doing work.

Before you rely on the answer

Assumptions and Limitations

  • Torque and RPM refer to the same operating point.
  • Unit conversion uses the selected horsepower convention.
  • Drivetrain loss is not included unless wheel or shaft measurements explicitly model it.

Practical tip

Using This Result in Practice

When comparing vehicles, check whether published figures are crank horsepower or wheel horsepower. Mixing the two can make one vehicle appear stronger simply because the measurement point is different.

Related calculations

Useful Calculations to Continue With

If you know engine horsepower and want an estimate after drivetrain loss, use the Wheel Horsepower Calculator.

If torque itself is the unknown quantity from force and lever arm, use the Torque Calculator.

Common questions

Horsepower Calculator FAQ

Why does the 5252 constant appear in horsepower formulas?

It comes from the conversion between lb-ft, revolutions per minute and the historical horsepower definition.

Is horsepower the same as torque?

No. Torque is rotational force; horsepower is power and depends on both torque and rotational speed.

Is one horsepower exactly 746 watts?

Mechanical horsepower is approximately 745.7 watts. Other horsepower definitions, such as metric horsepower, differ slightly.