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.