Horsepower to Kilowatts Formula
Multiply mechanical horsepower by 0.7457 to get kilowatts.
kW = hp × 0.7457
How it works
Both units measure power, meaning energy moved per unit of time, so the conversion between them is a fixed ratio rather than anything that depends on the engine. Mechanical horsepower was defined by James Watt as 550 foot-pounds per second, chosen so he could sell steam engines by comparison with the draft horses they replaced. In SI units that works out to exactly 745.6999 watts, so one horsepower is 0.7457 kilowatts and one kilowatt is 1.34102 horsepower. The trap is that there is more than one horsepower. Continental European manufacturers have long quoted metric horsepower, written PS or CV, defined as 75 kilogram-force metres per second, which is 735.49875 watts — about 1.37% smaller than the mechanical horsepower used in Britain and the United States. A car advertised as 150 PS is 147.9 hp, or 110.3 kW. The difference is small enough to look like rounding and large enough to matter when two specification sheets are being compared directly. One further caution: a quoted figure is usually peak power at a particular engine speed, whereas continuous rating is what a motor can sustain indefinitely. Electric motors in particular are often quoted at both, and the two can differ by a factor of two or more.
Variables
- kWPower in kilowatts (result)
- hpMechanical horsepower (input)
Worked examples
| Input | Result |
|---|---|
| 1 hp | 0.7457 kW |
| 200 hp | ≈ 149.1 kW |
| 500 hp | ≈ 372.85 kW |
Practical applications
- Comparing a European specification sheet in kW or PS against a US one in hp
- Sizing an electric motor, pump or generator, which are almost always rated in kilowatts
- Putting an electric vehicle and a combustion car on the same scale — 100 kW is about 134 hp
- Estimating running cost, since electricity is billed in kilowatt-hours
Common mistakes
- Confusing mechanical horsepower with metric PS or CV. They differ by about 1.37%.
- Comparing a peak figure against a continuous rating. Electric motors are commonly quoted at both.
- Confusing power with energy. A kilowatt is a rate; a kilowatt-hour is a quantity.
- Assuming brake horsepower at the crank equals power at the wheels. Transmission losses are typically 10 to 15%.
Used in
Use it in a tool
FAQs
Which horsepower is this?+
Mechanical horsepower (550 ft·lb/s). Metric horsepower (PS) is slightly smaller — 1 PS = 0.7355 kW.
What's a typical car?+
A modern compact car has ~150 hp ≈ 112 kW. A Tesla Model 3 Performance is ~510 hp ≈ 380 kW.