Horsepower and torque calculator
Power and torque are linked by engine speed. Enter the torque and RPM to get horsepower, kilowatts and metric horsepower, or enter the power and RPM to get the torque in newton metres and pound-feet.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose whether to find power or torque.
- Enter the engine speed in rpm.
- Enter the known value and pick its unit.
- Read the result in all the common units.
How it works
- Power in watts = torque in N·m × rpm × 2π ÷ 60.
- 1 lb·ft = 1.3558179 N·m; 1 hp = 550 ft·lbf/s = 745.69987 W; 1 PS = 735.49875 W.
- So hp = lb·ft × rpm ÷ 5252.11 and kW = N·m × rpm ÷ 9549.30.
- Torque from power runs the same formula backwards.
Worked example
400 N·m at 5,000 rpm: power = 400 × 5,000 × 2π ÷ 60 = 209,440 W = 209.4 kW = 280.9 hp = 284.8 PS. The other way, 150 hp at 5,000 rpm needs 150 × 33,000 ÷ (2π × 5,000) = 157.6 lb·ft, or 213.6 N·m.
Tips
- Torque is measured, power is calculated. Dyno sheets compute power from torque and RPM in just this way.
- Check the RPM. The same torque at twice the RPM is twice the power.
- Watch for crank and wheel figures. Wheel power is lower than engine power because of drivetrain losses.
Frequently asked questions
What is the formula linking horsepower and torque?
Power = torque × angular speed. In pound-feet and horsepower, hp = lb·ft × rpm ÷ 5252 (more exactly 5252.11). In newton metres and kilowatts, kW = N·m × rpm ÷ 9549 (more exactly 9549.30).
Why do the torque and power curves cross at 5252 rpm?
When torque is in lb·ft and power in hp, the formula has the constant 5252.11 in the denominator. At 5252 rpm the numbers are equal, so power and torque lines cross there on a dyno chart in those units.
Which horsepower is used?
Mechanical (imperial) horsepower, 745.7 W, is shown as hp, and metric horsepower (PS, CV, PK), 735.5 W, as PS. The tool uses their exact definitions in watts.
Why do my results differ slightly from the 5252 shortcut?
The shortcuts are rounded constants. This tool uses the unrounded values, which differ by a few thousandths of a percent.