kW, hp and PS – the difference and conversion formulas

Three units, three definitions

The kilowatt comes from the SI system (1 kW = 1,000 W) and expresses any power — engines and water heaters alike. Metric horsepower (German PS) was historically defined as the power to lift 75 kg by one meter per second, which is exactly 735.49875 W. British-American mechanical horsepower is defined in pounds and feet and equals 745.7 W.

The PS-vs-HP gap is about 1.4% — small enough to ignore in conversation, large enough that the same car's specs differ by a few "horses" between European and American sources.

Conversion formulas

PS = kW ÷ 0.73549875 · kW = PS × 0.73549875 · 1 kW ≈ 1.341 HP

For quick mental math: multiply kilowatts by 1.36 to get PS (66 kW ≈ 90 PS, 74 kW ≈ 100 PS, 110 kW ≈ 150 PS). In reverse, multiply horsepower by 0.74.

Why registration papers use kW

The kilowatt is the official unit across Europe, so registration documents, insurance policies and vehicle taxes use kW. Horsepower survives in everyday speech and marketing — "150 horses" sounds more tangible than "110 kilowatts" — but the legally relevant figure is always the kW one.

When importing a car from the US, note that an HP spec is neither the number that will appear in a European registration in kW, nor equal to metric PS.

Table of common power figures

Exact values for the power figures most often seen in registration papers — from city cars to stronger diesels. For anything else, the converter computes both directions as you type.