kW to HP Converter
Convert between Kilowatt (kW) and Horsepower (HP/PS).
Kilowatts, PS, and horsepower: three units, three definitions
There is no single horsepower. Metric PS, mechanical hp, and electrical horsepower are all different, and a car advertised at 150 PS is not 150 hp. The gap is small enough to look like rounding and large enough to change a specification.
Formula
PS = kW x 1.35962 | kW = PS x 0.735499 | hp (mechanical) = kW x 1.34102
One metric PS is defined as 75 kilogram-force metres per second, which works out to exactly 735.49875 watts.
Where horsepower came from, and why there are several
James Watt devised the unit in the 1780s to sell steam engines against draught horses. He estimated a mill horse could turn a 24-foot wheel 2.5 times a minute against a 180 pound force, which he rounded to 33,000 foot-pounds per minute.
That figure became mechanical horsepower, equal to 745.7 watts. Continental Europe defined its own version in metric terms - 75 kgf-m/s, or 735.5 watts - which became Pferdestarke in German and cheval-vapeur in French.
The 1.4% difference between them is small, but it is systematic. A 400 PS engine is 394 hp, and a 400 hp engine is 406 PS. Manufacturers quote whichever figure suits the market.
The units in current use
- Kilowatt (kW): the SI unit and the legally required one for type approval in the EU. 1 kW = 1,000 watts.
- Metric PS (also CV, pk, hk, ch): 735.49875 W exactly. Standard in continental Europe and Japan.
- Mechanical horsepower (hp, bhp): 745.6999 W. Standard in the UK and US.
- Electrical horsepower: 746 W exactly, used for motor ratings in the US.
- Boiler horsepower: 9,809.5 W, an entirely different quantity relating to steam generation. It is not comparable to the others.
Measurement standard matters more than the unit
Where the power is measured changes the figure more than which unit it is expressed in.
Brake horsepower is measured at the crankshaft, before losses through the gearbox and driveline. Wheel horsepower is measured at the driven wheels and is typically 10 to 15% lower for a manual transmission, more for an automatic or all-wheel drive.
Test standards also differ. Modern European figures follow ECE R85 or UN regulations, while SAE J1349 and SAE J2723 govern certified US figures. Before SAE net ratings were introduced in 1972, US manufacturers quoted gross figures measured without alternator, water pump, or exhaust system, which inflated numbers by 20% or more.
When comparing two cars, confirm both figures use the same standard. A pre-1972 US gross figure against a modern net figure is not a like-for-like comparison.
Worked example
A car is advertised at 150 PS. In kilowatts: 150 x 0.735499 = 110.3 kW. In mechanical horsepower: 110.3 x 1.34102 = 147.9 hp.
So 150 PS is 148 hp - a difference of about 2 hp that is entirely a unit artefact and represents no difference in the engine.
Going the other way, a 300 hp engine is 300 x 0.7457 = 223.7 kW, which is 304.2 PS. Quoting it as "300 PS" in a European market would understate it by 4 PS.
Power units in watts
| Unit | In watts | Used in |
|---|---|---|
| kilowatt (kW) | 1,000 | SI, EU type approval |
| metric PS / CV / pk | 735.49875 | Continental Europe, Japan |
| mechanical hp / bhp | 745.6999 | UK, US |
| electrical hp | 746 | US motor ratings |
| boiler hp | 9,809.5 | Steam generation only |
Metric PS and mechanical hp differ by about 1.4%. Boiler horsepower is a different physical quantity and does not convert meaningfully.
Frequently Asked Questions
Related calculators
References
- BIPM - The International System of Units (SI Brochure, 9th edition)
- UNECE Regulation No. 85 - measurement of net power
Last reviewed: 2026-08-07. This page is informational. For legal, medical, tax, or financial decisions, confirm the result with a qualified professional.