Horsepower to Kilowatts conversion

Horsepower to kilowatts

Kilowatts are the SI unit of power and the figure required on official documents, insurance forms and registration papers in most countries. Since one mechanical horsepower is 745.7 watts, 1 hp = 0.7457 kW: multiply horsepower by 0.7457. If the figure is in metric horsepower (PS or CV), the factor is 0.7355 instead.

Quick estimate

Take three quarters: 200 hp → 150 kW (149.1 exactly). For a closer figure subtract another half a percent.

• 1 hp = 0.75 kW
• 5 hp = 3.73 kW (a lawn-mower engine)
• 50 hp = 37.29 kW
• 100 hp = 74.57 kW
• 150 hp = 111.86 kW
• 200 hp = 149.14 kW
• 300 hp = 223.71 kW
• 500 hp = 372.85 kW
• 1000 hp = 745.7 kW

Where the number came from

James Watt defined the horsepower in the 1780s to sell steam engines to mine owners who were used to horses: the rate at which a horse could turn a mill wheel, which he put at 33 000 foot-pounds per minute. The unit named after him, the watt, replaced it in science, but horsepower never left the showroom.

Cars, boats and motors

Vehicle tax in several European countries is banded by kW, so buyers convert the advertised hp before choosing a trim level. Marine engines and outboards are sold in hp worldwide, while the electric motors replacing them are in kW; a 10 hp outboard is roughly a 7.5 kW electric. Industrial motors in the US carry both figures on the nameplate.

Power is not energy

A 100 hp engine running flat out for an hour uses 74.57 kWh of energy. Kilowatts describe how fast energy is delivered; kilowatt-hours describe how much. Electricity bills and EV batteries are in kWh, engine ratings in kW or hp.

Worked examples

A 250 hp V6. 250 × 0.7457 = 186 kW.

A 25 hp outboard. 25 × 0.7457 = 18.6 kW.

A 1 hp pool pump. 0.75 kW — running 8 hours a day it uses about 6 kWh.

Frequently asked questions

How many kW is 1 hp? 0.7457 kW (mechanical), 0.7355 kW (metric PS).

What is 300 hp in kW? 224 kW.

Does "bhp" convert differently? No — brake horsepower is measured at the crankshaft but it is the same unit, 745.7 W.

Related conversions

Kilowatts to horsepower reverses this page.

Good to know

Manufacturers measure horsepower under different standards, and the differences are bigger than the hp-to-kW rounding. SAE net figures (US) and DIN or EU figures are measured with accessories fitted and are broadly comparable; older SAE gross numbers from before 1972 were measured without them and read 15–25 % higher. Japanese cars were long quoted in PS under a voluntary 280 PS cap. When you convert an old American muscle-car figure to kilowatts, remember it was probably a gross rating. Also, peak power is quoted at a specific engine speed; a 200 hp engine at 6 500 rpm and a 200 hp engine at 4 000 rpm feel very different, because torque, not power, is what you notice when accelerating from low revs.