Horsepower to kW:
multiply by 0.7457

How many kilowatts are in a horsepower?

One mechanical horsepower is 0.7456998716 kilowatts, which is about 745.7 watts. Remember it as roughly three quarters of a kilowatt. The unit is still used for engines, mowers, pumps and electric motors, especially in the US.

The mechanical horsepower comes from 550 foot-pounds of work per second. The kilowatt is the SI unit of power, so most specifications outside the US are written in kW instead.

The hp to kW formula

A second example runs the other way. A 100 kW electric motor is 100 × 1.34102209 = 134.1022 hp, so replacing a 125 hp motor with a 100 kW one gives slightly more power than you may expect.

Chart: horsepower to kW

For other values, combine rows. An 80 hp engine is 50 hp plus 25 hp plus 5 hp, so 37.28499358 + 18.64249679 + 3.728499358 = 59.65598973 kW.

Where hp to kW is used

• Car specifications: manuals and listings in some countries give kW, while others still advertise horsepower.
• Lawn mowers and generators: a 5 hp petrol engine is about 3.73 kW.
• Electric motors and pumps: a 5 hp motor in a US catalogue is about 3.73 kW, which helps in matching it to a kW-rated drive.
• Marine engines: outboards may be rated in hp or kW depending on the market.

Rated power is not always delivered power

A power rating on a label does not mean the machine gives that much at the wheels or at the shaft. A car engine rated at 150 hp loses some power in the gearbox and driveline, so the power reaching the wheels is lower. Motor nameplates, on the other hand, usually state output at the shaft.

When you compare two machines, make sure both are rated the same way and in the same horsepower unit. Converting both to kW removes one source of confusion.

A short worked check with a pump motor

A pump catalogue lists a 15 hp motor, but your drive is rated in kW. Multiplying gives 15 × 0.7456998716 = 11.1855 kW. Because 0.7457 is close to three quarters, a quick check is 15 × 0.75 = 11.25 kW, which agrees to within 1 percent. Choose a drive rated at or above the exact figure, not below it.

Common mistakes with hp and kW

• Using metric horsepower. A PS or CV is about 735.5 W, so a car marked 100 PS is 73.55 kW, not 74.57 kW.
• Dividing hp by 0.7457 when you should multiply. Horsepower is a larger unit than the kilowatt, so the kW number is the smaller one.
• Confusing electrical and mechanical horsepower. The electrical horsepower used in some US motor ratings is exactly 746 watts, a tiny difference.
• Mixing torque and power. Torque is measured in newton metres or pound-feet, and is not the same as horsepower.