Guide

Comparing engine power: kW, PS and hp

Vehicle datasheets state power in kW, PS or hp — and the three are not equal. Between metric horsepower and mechanical horsepower there is about one percent, between PS and kW a factor of about 1.36.

Horsepower is a defined unit, not a measurement

Horsepower traces back to early attempts to measure the power of draught animals, but today it is defined exactly: 1 PS = 735.49875 W. It is not a statement about how many horses an engine replaces.

PS and hp are different units

Metric horsepower (PS) and mechanical horsepower (hp) were fixed using different foot and pound definitions: 1 PS = 735.49875 W, 1 hp = 745.6998715823 W. The difference is about 1.4 %. An engine rated 150 PS produces about 110 kW, one rated 150 hp about 112 kW.

Why kW is the most unambiguous figure

The kilowatt belongs to the International System of Units and traces back to the base units through the watt. PS and hp, by contrast, are historically grown units whose definitions differ by region. For comparing vehicles from different countries kW is therefore the most reliable common basis.

Torque is a different quantity

Power and torque are often quoted together but are not the same. Torque describes force at a lever arm, power additionally involves rotational speed. At equal power more torque means lower speed and vice versa. The unit of torque is the newton metre, not the watt.

Matching conversions

Matching tables

Unit family: Power

Sources