Mechanical horsepower to kilowatts (hp to kW)

One mechanical horsepower is exactly 550 foot-pounds per second, which is 745.6998715822702 watts, exact in principle, since the foot and the pound-force are both exact.

Worked through: 150 hp x 0.745699872 = 111.855 kW.

Going the other way, one kilowatt is 1.34102209 mechanical horsepower.

For mental arithmetic: Multiply by 0.75 and take off a little; three quarters is within 0.6%.

There are two horsepowers and they differ by 1.4%. Mechanical or imperial horsepower is 745.7 W, defined by Watt from the rate a dray horse could raise a load. Metric horsepower (written PS in Germany, cv in France and Italy, ch elsewhere) is 735.5 W, defined as 75 kgf.m/s. A car quoted at 300 PS is 296 hp, and manufacturers quote whichever is larger for the market they are in. This converter offers both as separate units because they are separate units.

Precision is worth matching to the input. A measurement given as 1 hp carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.