Horsepower Converter (PS, HP, kW)

Understanding the horsepower converter — concept and principle

Horsepower is a traditional unit of power, but there are several versions. Korean, Japanese and European car specifications usually use metric horsepower (PS, called 마력 in Korean), US specifications use mechanical horsepower (hp), electric motors are sometimes rated in electric horsepower, and steam boilers used boiler horsepower. This converter switches between all of them and the SI units, kilowatts and watts.

How it is calculated

The value is converted to watts and then to the target unit: result = value × (W per source unit) ÷ (W per target unit). The definitions are:

• 1 PS = 75 kgf·m/s = 75 × 9.80665 = 735.49875 W (exact)
• 1 hp (mechanical) = 550 ft·lbf/s = 745.6998716 W
• 1 electric hp = 746 W (exact)
• 1 boiler hp ≈ 9,809.5 W
• 1 kW = 1,000 W

The principle

Power is work done per unit of time. James Watt introduced the horsepower to compare steam engines with the horses they replaced, settling on 33,000 foot-pounds per minute (550 ft·lbf/s). When metric countries adopted the idea, they rounded it to lifting 75 kilograms by one metre in one second, which is about 1.4% smaller. Both are defined through force and distance, so converting them to watts uses standard gravity (9.80665 m/s²) and the exact foot and pound. Boiler horsepower is different in nature: it measures the rate of steam production, which is why it is about 13 times larger.

Worked example

1. Inputs: 200 PS, convert to kilowatts.
2. 200 × 735.49875 W = 147,099.75 W.
3. Divide by 1,000: 147.09975 kW.
4. In mechanical hp: 147,099.75 ÷ 745.6998716 = 197.2640141 hp.
5. In electric hp: 147,099.75 ÷ 746 = 197.1846515; in boiler hp: 14.99564198.

How to read the result

For quick estimates, kW ≈ PS × 0.735 and PS ≈ kW × 1.36, while hp ≈ PS × 0.986. The difference between PS and hp is small, about 3 units at 200, but it matters when comparing official figures. Car power is usually measured at the crankshaft on a test bench; power at the wheels is lower because of drivetrain losses. Electric vehicles are typically rated in kW, so converting to PS lets you compare them with combustion cars.

Common mistakes

• Treating PS and hp as identical in precise comparisons.
• Confusing power (kW, PS) with torque (N·m, kgf·m); they are different quantities.
• Comparing a wheel horsepower figure with a crankshaft figure.
• Using boiler horsepower for engines or motors.

Frequently asked questions

Is PS the same as hp?

No. 1 PS = 0.98632 hp, so PS is slightly smaller.

How do I convert kW to PS?

Multiply by 1.35962. For example, 100 kW ≈ 136 PS.

What does BHP mean?

Brake horsepower, the power measured at the engine's output shaft on a dynamometer, before drivetrain losses.

Sources: NIST Special Publication 811 (2008), Appendix B · BIPM, The International System of Units (SI Brochure), 9th edition