Horsepower, torque, rpm, kilowatts and metric horsepower
Updated October 2026
Pick horsepower from torque and rpm when you have a torque reading at a specific engine speed, for example from a dyno sheet or a published torque curve. Pick torque from horsepower and rpm to work backward from a power figure. Pick convert to turn horsepower into kilowatts and metric horsepower. Torque is in pound-feet. The drivetrain loss is your own estimate, used only for the wheel-horsepower line. Results show horsepower, kW, PS, torque in lb-ft and N·m, and estimated wheel horsepower.
One horsepower is defined as 550 foot-pounds of work per second, or 33,000 per minute. Torque times engine speed in radians per minute gives power in foot-pounds per minute, and dividing 33,000 by 2π (the radians in one revolution) gives 5,252.1. Below 5,252 rpm an engine’s torque number is higher than its horsepower number; above it, horsepower is higher.
Worked example: 300 lb-ft at 5,500 rpm is 300 × 5,500 ÷ 5,252.1 = 314.16 hp. Multiply by 0.7457 for 234.27 kW, or by 745.7 ÷ 735.5 for 318.5 PS. With a 15% drivetrain loss estimate, wheel horsepower is about 267.0 hp.
| RPM | Horsepower | kW |
|---|---|---|
| 2,000 | 114.2 | 85.2 |
| 3,000 | 171.4 | 127.8 |
| 4,000 | 228.5 | 170.4 |
| 5,252 | 300.0 | 223.7 |
| 6,000 | 342.7 | 255.6 |
| 7,000 | 399.8 | 298.2 |
The same torque makes more power at higher rpm. Real engines do not hold constant torque across the range, so read actual values off the engine’s curve.
| Unit | Equals |
|---|---|
| 1 mechanical horsepower (hp) | 745.7 W = 1.0139 PS |
| 1 metric horsepower (PS) | 735.50 W = 0.9863 hp |
| 1 kilowatt (kW) | 1.3410 hp = 1.3596 PS |
| 1 lb-ft of torque | 1.3558 N·m |
| 300 PS | 295.9 hp |
Manufacturers rate engines at the crankshaft. A chassis dynamometer measures at the wheels, after the transmission, driveshaft and differential take their share. There is no fixed loss percentage: it depends on the drivetrain, the dyno and the test conditions, so the 15% default is only a placeholder and wheel horsepower from this calculator is an estimate. Metric horsepower (PS), used in Europe, is slightly smaller than mechanical horsepower: 735.5 W versus 745.7 W.
Multiplying peak torque by peak-power rpm. Peak torque and peak horsepower happen at different engine speeds, so that product overstates power. Mixing PS and hp. A European 300 PS rating is about 296 hp. Using N·m with the 5,252 constant. Convert to lb-ft first (divide by 1.3558) or use kW = N·m × rpm ÷ 9,549. Comparing dyno numbers from different shops: dyno type and correction factors differ, so compare before-and-after runs on the same dyno. Reading a torque graph above 5,252 rpm and expecting torque to exceed horsepower there: it cannot.