Horsepower vs. Kilowatts: Comparing Engine Power Across Countries
How horsepower and kilowatts both measure power, why European car specifications list kilowatts while others list horsepower, and why different definitions of horsepower can give slightly different converted figures.
Published
Horsepower and kilowatts both measure power — the rate at which work is done or energy is transferred — not energy itself. One mechanical horsepower is approximately 0.746 kilowatts. The reason car listings sometimes show one unit and sometimes the other comes down to which measurement system a country's vehicle regulations are based on.
Where horsepower came from
James Watt, the 18th-century Scottish engineer, coined the term "horsepower" to market his improved steam engines by comparing their output to the working rate of a horse. The unit stuck, long after steam engines gave way to internal combustion and electric motors, and it remains the default way car power is described in the US and several other countries.
Why Europe uses kilowatts
The European Union's official vehicle specifications use the metric system, so engine power is legally expressed in kilowatts. Many European manufacturers still list horsepower (or its metric cousin, PS/CV) alongside kW in marketing material, since horsepower remains a more intuitive number for most consumers.
Not all horsepower is equal
Several historical definitions of horsepower exist, and they don't all convert identically:
| Definition | Equal to | Used in |
|---|---|---|
| Mechanical horsepower (hp) | ≈ 745.7 watts | US and UK vehicle and engine specifications |
| Metric horsepower (PS or CV) | ≈ 735.5 watts | Much of continental Europe |
| Electrical horsepower | Exactly 746 watts | Electrical engineering contexts |
The differences are small enough to ignore for casual comparisons, but they explain why converting a manufacturer's quoted horsepower figure to kilowatts (or vice versa) can land a few tenths off from another source's number.
Frequently asked questions
- How many kilowatts is 100 horsepower?
- 100 mechanical horsepower is approximately 74.6 kilowatts, using the standard conversion of 1 hp ≈ 0.746 kW.
- Why do European car specifications list power in kW?
- The European Union uses the metric system for official vehicle specifications, so power output is measured in kilowatts. Many European manufacturers list both kW and hp (or PS, the metric horsepower variant) since horsepower remains familiar to consumers.
- Is horsepower a unit of energy or power?
- Power. Horsepower measures the rate at which work is done (like watts), not the total amount of energy. It was originally defined by James Watt to compare the output of steam engines against the working rate of a horse.
- Are all 'horsepower' units the same?
- No. Mechanical horsepower (hp), metric horsepower (PS or CV), and electrical horsepower differ slightly — metric horsepower is about 1.4% smaller than mechanical horsepower — so converted figures can vary slightly depending on which definition a manufacturer uses.