kW to HP Converter

How to convert kilowatts to horsepower

A kilowatt is 1,000 joules per second. Mechanical horsepower was defined by James Watt as 550 foot-pounds-force per second, the rate at which he estimated a mill horse could work. Using the exact foot (0.3048 m) and pound-force (4.4482216 N), 550 ft·lbf/s = 745.699872 W. One kilowatt therefore holds 1,000 ÷ 745.6999 = 1.341022 hp. The hp to kW converter runs that factor in reverse, and the power converter covers watts, megawatts and BTU per hour.

The trap is that "horsepower" is not one unit. Car specs in Europe and Asia often quote metric horsepower (PS, CV or pk), which is about 1.4% smaller, so the same 100 kW engine is 134.1 hp but 136 PS. This converter defaults to mechanical hp, the US and UK standard; for PS or electrical horsepower, use the Horsepower switch above.

Step by step

1. Take the power in kilowatts.
2. Multiply by 1.34102 (or divide by 0.7457).
3. For metric PS instead, multiply by 1.35962.
4. Round to the nearest whole hp, as spec sheets do.

See it on a scale

What is the difference between peak and continuous power in an EV?

An EV's headline kW figure is usually its peak output, available for a few seconds when the battery and motor are cool. Electric motors can also run at a lower continuous rating indefinitely. European type approval under UN Regulation No. 85 records both the maximum net power and a maximum 30-minute power for electric drivetrains, and the gap between them can be large.

Do not confuse the motor's kW with the battery's kWh. A 150 kW motor fed by a 60 kWh battery could, in theory, drain it in 24 minutes at full power. The first number is a rate, the second an amount of energy. For energy conversions, the kWh to BTU converter is the right tool.

Why EVs feel quicker than the hp suggests

Electric motors deliver high torque from zero rpm, so an EV with the same peak kW as a gasoline car often accelerates harder off the line. The kW figure is still a fair comparison of top-end power.

What is the difference between bhp, wheel hp and net hp?

Brake and net horsepower are both measured at the crankshaft, net with every production accessory fitted, while wheel horsepower is measured at the driven wheels and always comes out lower.

• Brake horsepower (bhp) is measured at the engine's crankshaft on a dynamometer. Most manufacturer figures are brake power.
• Wheel horsepower (whp) is measured at the wheels on a chassis dyno and is lower because the transmission and driveline absorb power. A loss of about 10 to 20% is a common rule of thumb.
• SAE net horsepower (SAE J1349) is measured with all production accessories fitted and corrected to standard air conditions. US ratings have used net figures since the early 1970s, so older gross ratings look higher.

Converting kW to hp does not change which of these you have. A kW figure measured at the crank converts to crank horsepower. When comparing speed specs from Europe as well, the km/h to mph converter helps.

How do you convert kW to hp in your head?

Multiply by 4, divide by 3. For 150 kW: 150 × 4 ÷ 3 = 200 hp, against the exact 201.2 hp. The shortcut runs about 0.6% low, which is well inside the variation between two dyno runs. For PS, add 36% to the kW figure: 150 × 1.36 = 204 PS, exactly matching 203.9 PS to the nearest unit.

• Do not divide by 0.746 for car engines if the spec says PS; divide by 0.7355 instead.
• Electric motors in the US are often nameplated in hp using 746 W. The difference from mechanical hp is only 0.04%.
• Watts, not kilowatts? Divide by 1,000 first with the watts to kW converter.