PS, HP and kW Conversion Chart

PS and horsepower are not the same unit. One kilowatt is 1.3410 mechanical horsepower and 1.3596 metric horsepower, so a PS figure is about 1.4 per cent higher than the hp figure for the same engine. One PS is 0.98632 hp. The tables below carry all three units in every row so the gap is visible rather than assumed.

Three units, two definitions

Mechanical horsepower — the one written hp, and the one meant in the United States and Britain — is defined as 550 foot-pounds per second, which works out at 745.7 watts. Metric horsepower, written PS in Germany, CV in France and Spain and pk in the Netherlands, is defined as 75 kilogram-metres per second, which is 735.5 watts. They were arrived at independently and they were never the same number.

The practical consequence is that the same engine is honestly quoted at two different figures depending on where the brochure was printed, with the European one always the larger. A European specification listing 150 PS is 148 hp, not 150 hp, and a car sold at 200 hp in the United States is 203 PS in Germany. Neither figure is an error and neither is a rounding.

Kilowatts to horsepower and PS

PS to horsepower and kilowatts

Method and precision

Mechanical horsepower is 1.341022 per kilowatt and metric horsepower is 1.359622 per kilowatt; both derive from SI definitions and neither is an approximation of the other. The PS to hp factor above is the ratio of those two, 0.986320, rather than a third constant that could drift from them. Table values are rounded to one decimal place for display only.

Which figure is on the paperwork

Type approval and registration documents across Europe are stated in kilowatts, because that is the SI unit and the only one with a single definition. PS appears alongside it because buyers are used to it. If a number has to be compared across markets, convert both sides to kilowatts first — it is the only one of the three that means exactly one thing everywhere, and it removes the question of which horsepower somebody meant.

The kilowatt-to-horsepower tables are broken out separately in the kilowatts to horsepower chart. Vehicle work is in automotive tools.