kW to hp and PS converter: kilowatts and both horsepowers

Two horsepowers and a kilowatt

A truck’s data sheet can give its engine power in three units. The kilowatt is the SI unit. The metric horsepower, written PS on German and Turkish sheets, CV on Spanish ones and л.с. on Russian ones, is 735.4988 W. The horsepower of NIST’s table, defined as 550 foot-pounds-force per second and written hp, is 745.6999 W, about 1.4 % more. One horsepower figure therefore gives two different kilowatt values, depending on which horsepower it is:

• 500 PS = 367.7 kW = 493.2 hp
• 500 hp = 372.8 kW = 506.9 PS

Which horsepower a sheet means

The kilowatt figure beside it settles the question. Volvo Trucks UK lists the Volvo FH’s D13 at 500 hp and 368 kW; 368 kW is 500.3 PS but 493.5 hp, so that “hp” is the metric horsepower. Ford Trucks prints the F-MAX’s single rating as 510 PS and 375 kW, and 375 kW is 509.9 PS. A figure given in horsepower alone cannot be converted until it is clear which unit it is: the Freightliner Cascadia page on this site quotes Freightliner’s ratings in HP only, with no kilowatts.

The formulas

Convert	Multiply by	Inverse
PS to kW	0.7354988	kW to PS: × 1.359622
hp to kW	0.7456999	kW to hp: × 1.341022
PS to hp	0.986320	hp to PS: × 1.013870

The first two factors are NIST’s; the others are their quotients and reciprocals (our arithmetic).

Where the factors come from

NIST Special Publication 811, Appendix B.8, lists “horsepower (550 ft · lbf/s)” as 7.456 999 × 10² W and “horsepower (metric)” as 7.354 988 × 10² W, both to seven significant digits. The calculator uses them as printed and rounds only the result it displays. NIST lists other horsepowers as well (electric, boiler, U.K. and water); none of them is the unit of a truck data sheet’s PS, CV or л.с., and the calculator leaves them out.