Comparison

Kilowatts vs Horsepower

Two ways to talk about engine power — one SI, one steam-age marketing.

Kilowatt (kW)Horsepower (hp)
Definition1,000 J/s (SI)550 ft·lb/s (mechanical)
1 kW= 1 kW≈ 1.341 hp
Typical EV motor150 kW≈ 201 hp
Used inEU spec sheets, electric motorsUS car ads, ICE engines
Kilowatt (kW) pros
  • SI standard
  • Direct compatibility with electrical units
Horsepower (hp) pros
  • Familiar to US car buyers
  • Aligned with century of automotive marketing

When to use which

Use Kilowatt (kW)

Use kW for industrial motors, EV ratings, and anything electrical.

Use Horsepower (hp)

Use hp for traditional automotive specs and US power tools.

Historical context

James Watt coined horsepower in the 1780s as a marketing device rather than a unit of physics. He needed a way to tell mine owners how many draft horses one of his steam engines would replace, and settled on 550 foot-pounds per second. The irony is that the SI unit of power was later named after him, so the two units on this page are both Watt's legacy. Mechanical horsepower works out to 745.6999 watts, making one horsepower 0.7457 kW and one kilowatt 1.34102 hp. A complication arrived from continental Europe, which defined its own metric horsepower — written PS in Germany or CV in France — as 75 kilogram-force metres per second, or 735.49875 watts. That is 1.37% smaller than mechanical horsepower, so a car advertised as 150 PS is 147.9 hp. The rise of electric vehicles has quietly pushed kilowatts into consumer use, since motors and chargers have always been rated that way.

Practical recommendation

Use kilowatts. It is the SI unit, it avoids the mechanical-versus-metric horsepower ambiguity entirely, and it is already the unit for electric motors, generators, chargers and your electricity bill. Horsepower is worth keeping only where the audience expects it, which in practice means combustion-engine car specifications for British and American readers. If you are comparing two specification sheets, check which horsepower each one means before concluding that one engine is stronger — and check whether the figure is peak or continuous, which on electric motors can differ by a factor of two.

Related tools

Horsepower to kW formulaEnergy converter

FAQs

Why three different horsepowers?+

Mechanical hp (745.7 W), metric PS (735.5 W), and electrical hp (746 W) all exist. Most US specs mean mechanical.

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