Horsepower Calculator: Torque, RPM and Power
Find horsepower from torque and rpm, torque from horsepower, or the engine speed, with P = T × 2πn / 60. Converts kW, hp and PS and shows the 5,252 rpm crossover.
Fill in all but one field: the empty field is the one you solve for.
Results are at the crankshaft. Wheel horsepower is lower because the gearbox, driveshaft and tyres lose some power on the way.
| Torque unit | Power unit | Crossover |
|---|---|---|
| lb·ft | hp | 5,252.11312203 rpm |
| N·m | PS | 7,023.49570202 rpm |
| N·m | kW | 9,549.29658551 rpm |
About the Horsepower Calculator
The Horsepower Calculator links the three numbers on an engine's spec sheet: power, torque and engine speed. Fill in any two and leave the third empty, and the calculator solves it. Power can be typed in mechanical horsepower (hp), metric horsepower (PS), kilowatts or watts, torque in pound-feet, newton-metres or pound-inches, and the engine speed in revolutions per minute. A power converter turns one power figure into all four units, and a crossover table shows the engine speed where the torque and power numbers are equal.
Results are at the crankshaft, the figures a manufacturer quotes. Wheel horsepower measured on a chassis dynamometer is lower, often by 10 to 20 percent, because the gearbox, driveshaft, differential and tyres all lose some power on the way.
How to use it
Torque to horsepower
Type the torque, pick its unit, and type the engine speed. Leave the power field empty and choose the unit you want the answer in.
Horsepower to torque
Type the power and the engine speed and leave the torque field empty. This is how you work out the torque behind a peak power figure, such as 400 hp at 6,000 rpm.
Power converter
Choose Power converter, type a power and pick its unit. The calculator shows the same power in W, kW, hp and PS.
The formula
Power is torque times angular speed. With n in revolutions per minute, the angular speed is 2πn / 60 radians per second:
The calculator works in SI units, watts, newton-metres and rpm, and converts at the edges. One mechanical horsepower is 745.69987158227022 W, one metric horsepower (PS) is 735.49875 W, and one pound-foot is 1.3558179483314004 N·m. Results are printed to 12 significant digits.
Worked examples
- 300 lb·ft at 5,000 rpm. P = 300 × 5,000 ÷ 5,252.11 = 285.599332145 hp.
- 400 hp at 6,000 rpm. T = 400 × 5,252.11 ÷ 6,000 = 350.140874802 lb·ft.
- 400 N·m at 3,000 rpm. P = 400 × 2π × 3,000 ÷ 60 = 125,663.7 W, or 125.663706144 kW.
- 300 hp with 350 lb·ft. n = 300 × 5,252.11 ÷ 350 = 4,501.81124746 rpm.
Why 5,252 rpm?
With torque in lb·ft and power in hp, the formula becomes hp = lb·ft × rpm ÷ 5,252.11. At exactly 5,252.11 rpm the two numbers are equal, which is why the torque and power curves of every dyno chart in these units cross there. With N·m and PS they cross at 7,023.5 rpm, and with N·m and kW at 9,549.3 rpm.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device.
Related tools
Convert power units directly with the kW to HP Converter, relate force and distance with the Work Calculator, or work out electrical power with the Ohm's Law Calculator.
Frequently asked questions
How do I convert torque to horsepower?
Multiply the torque in lb·ft by the engine speed in rpm and divide by 5,252.11. In SI units, multiply the torque in N·m by 2π times the rpm and divide by 60 to get watts.
How do I find torque from horsepower?
Multiply the horsepower by 5,252.11 and divide by the engine speed in rpm to get lb·ft. For example, 400 hp at 6,000 rpm needs about 350.1 lb·ft of torque.
Why do torque and horsepower curves cross at 5,252 rpm?
With torque in lb·ft and power in hp, the conversion constant is 33,000 ÷ 2π, which is 5,252.11. At that speed the two numbers are equal, so the curves on a dyno chart always cross there.
What is the difference between hp and PS?
Mechanical horsepower is 745.7 W and metric horsepower, PS, is 735.5 W, so one PS is about 1.4 percent less than one hp. European car makers often quote PS.
Is this crankshaft or wheel horsepower?
The calculator gives power at the crankshaft, where torque is measured on an engine dynamometer. Wheel horsepower is lower because the gearbox, driveshaft and tyres lose part of the power.
Why must every value be greater than zero?
An engine at zero rpm or with zero torque makes no power, and solving for a missing value would divide by zero. The calculator therefore asks for positive values only.