kW to PS Converter

This trips up a surprising number of converters, so it is worth stating plainly. Metric horsepower (PS) and mechanical horsepower (hp) are different units that happen to share a name in translation.

PS comes from a metric definition: 75 kilogram-force metres per second, which is exactly 735.49875 watts. Mechanical hp comes from an imperial one: 550 foot-pounds-force per second, which is about 745.7 watts.

The gap is about 1.39 percent. On a 150 PS engine that is roughly two horsepower, small enough to look like a rounding artefact and large enough to be wrong. A car advertised at 150 PS is 147.9 hp, not 150 hp.

One PS is exactly 0.73549875 kW, because the definition rests on standard gravity, which is itself defined as exactly 9.80665 m/s². Multiply 75 kilograms by that figure and you get 735.49875 watts, with no rounding anywhere.

Inverted, one kilowatt is 1.359621617 PS. One kilowatt is 1.34102209 hp. One hp is 1.013869665 PS.

NIST publishes both horsepower factors rounded to seven significant figures, at 735.4988 W and 745.6999 W, which agree with the exact values above.

Germany and much of Europe formally moved to the kilowatt decades ago, and it is the kilowatt that appears in field P.2 of a German Fahrzeugschein and on every EU type approval.

PS persisted anyway, because a century of engines were sold on it. A driver who knows what 200 PS feels like has no instinct for 147 kW, even though they are the same car. Manufacturers print both, which is exactly why a converter is useful.