Kilowatts and horsepower measure the same thing — the rate of doing work — but they come from different traditions, and there is more than one kind of horsepower. Getting the conversion right means knowing which horsepower you are dealing with. This guide covers the formulas, the exact factors, and the common cases where the number you read is not the number you think it is.
The two horsepower definitions you will meet
Mechanical (imperial) horsepower — the one used in US and UK car specs — is defined as 550 foot-pounds per second, which equals exactly 745.7 watts. So 1 hp = 0.7457 kW, and 1 kW = 1.3410 hp.
Metric horsepower (PS, “Pferdestärke”) is defined as 75 kilogram-force metres per second, or 735.5 watts. It is the standard in much of Europe and Asia. Here 1 PS = 0.7355 kW, and 1 kW = 1.3596 PS.
The gap between them is about 1.4%. That sounds trivial until you compare a European spec sheet against an American one: a car listed at 100 kW is 136 PS in Germany but 134 hp in the United States. Same engine, two different numbers, neither wrong.
The formulas
hp = kW ÷ 0.7457 or hp = kW × 1.3410
PS = kW ÷ 0.7355 or PS = kW × 1.3596
Going the other way: kW = hp × 0.7457 and kW = PS × 0.7355.
Worked example: an electric motor rated at 7.5 kW. In mechanical horsepower that is 7.5 × 1.3410 = 10.06 hp. In metric PS it is 7.5 × 1.3596 = 10.20 PS. If you are sizing a replacement motor against a nameplate that says “10 hp,” you need roughly 7.46 kW — the rounding to 7.5 kW is fine, but rounding down to 7 kW would leave you short.
Common conversions
| kW | Mechanical hp | Metric PS | Typical use |
|---|---|---|---|
| 1 kW | 1.34 | 1.36 | Small power tool |
| 2.2 kW | 2.95 | 2.99 | domestic water pump |
| 5 kW | 6.71 | 6.80 | Workshop air compressor |
| 7.5 kW | 10.06 | 10.20 | Industrial motor |
| 11 kW | 14.75 | 14.96 | Level 2 EV charger bank |
| 75 kW | 100.6 | 102.0 | Small car engine |
| 150 kW | 201.2 | 203.9 | Performance EV motor |
| 300 kW | 402.3 | 407.9 | Supercar / small generator |
Our Power Converter handles kW, hp, PS, BTU/h and watts in one step if you would rather not do the arithmetic.
Where people get this wrong
Comparing EV range figures across markets. An EV sold in both Europe and the US may list identical kW but different “horsepower” on regional sites, purely from the definition used. The motor did not change.
Assuming engine kW equals wheel kW. Manufacturer figures are measured at the crank (or motor output). Drivetrain losses of 10–15% mean a 150 kW car typically delivers about 130 kW at the wheels. Dyno sheets that quote “wheel horsepower” will always look lower than the brochure, and the size of the gap says nothing about whether the car is healthy.
Mixing up electrical and mechanical ratings. On an AC motor nameplate, input electrical kW and output mechanical kW differ by the efficiency factor. A motor drawing 7.5 kW electrically at 90% efficiency delivers about 6.75 kW mechanically — roughly 9 hp, not 10.
Why EVs quote kW and older cars quote hp
Electric vehicle marketing leans on kilowatts largely because the motor’s electrical input is already measured that way, and because kW is the SI unit used in regulatory filings worldwide. Traditional engine marketing grew up with horsepower, and that convention stuck even in markets that otherwise use metric units. So you will routinely see a single EV listed as “150 kW” in a European brochure and “201 hp” in an American one, with no mechanical difference at all.
There is a second reason the kW figure can look impressive: electric motors deliver peak torque from zero rpm, so a modest kW rating can feel quicker off the line than a combustion engine with a higher peak power figure. Power and torque are related but distinct — power is torque multiplied by rotational speed — so comparing a single peak number across the two technologies tells you less than the same comparison within one technology.
When you see both figures quoted on the same vehicle, check whether the horsepower is mechanical or metric before comparing against another source. A 1.4% discrepancy will not change how a car drives, but it will make two reviews of the same car look like they disagree.
Key Takeaways
Kilowatts convert to horsepower at 1 kW = 1.3410 mechanical hp or 1.3596 metric PS — a 1.4% difference that matters when you compare specs across regions. Divide kW by 0.7457 for hp and by 0.7355 for PS. Watch for crank versus wheel figures and for electrical versus mechanical ratings, since both make the real output lower than the headline number.