Horsepower vs Kilowatts vs PS: Understanding Engine Power Ratings
Compare a European hatchback to an American truck and you will see engine power quoted as kW, PS, hp or bhp. They all measure the same thing, the rate at which an engine does work, but they are defined slightly differently. Here is how to compare them fairly.
The units
- Watt (W) and kilowatt (kW): the SI units of power. One kilowatt is 1,000 watts. Electric motors, new European specs and most science use kW.
- Mechanical horsepower (hp): 745.7 watts. Used in the US and UK for cars, motorcycles and engines.
- Metric horsepower (PS, CV, cv, ch): exactly 735.5 watts. Used in Germany (PS, from Pferdestärke), France (CV or ch), Japan and across Europe.
- Brake horsepower (bhp): mechanical horsepower measured at the engine’s output shaft, before losses in the gearbox and drivetrain.
Converting
- 1 kW = 1.341 hp = 1.360 PS
- 1 hp = 0.7457 kW = 1.014 PS
- 1 PS = 0.7355 kW = 0.986 hp
The kilowatts to horsepower and horsepower to kilowatts converters let you pick either type of horsepower.
Examples
| kW | hp | PS |
|---|---|---|
| 50 | 67 | 68 |
| 75 | 101 | 102 |
| 100 | 134 | 136 |
| 150 | 201 | 204 |
| 200 | 268 | 272 |
| 300 | 402 | 408 |
Power and torque are different
Power tells you how quickly an engine can do work and so how fast a car can go at its limit. Torque is the twisting force the engine produces, which governs how hard the car pulls away from a standstill or when towing. Power equals torque multiplied by rotational speed, which is why a small, high-revving engine can have the same power as a large, slow one but feel very different to drive.
Electric cars
Electric cars are almost always rated in kW. A 150 kW motor is about 201 hp. Because electric motors produce full torque from zero rpm, they often feel quicker than a combustion engine with the same power rating.
Home and workshop equipment
Motors on pumps, compressors and garage tools are often rated in horsepower, but be careful: some figures are “peak” or “developed” horsepower, which is much higher than the continuous power the motor can deliver. Compare the electrical input in watts when you can.