kW vs HP vs PS: Engine Power Units Finally Explained

Published on May 7, 2026 · 7 min read

Open any car spec sheet and you will see a confusing mix of units: kW, hp, bhp, PS, even CV. They all measure the same thing — power — but were defined by different industries in different centuries. This guide finally untangles them.

The four power units you will meet

• Watt (W) and kilowatt (kW): SI units. 1 kW = 1,000 watts.
• Mechanical horsepower (hp): 745.6999 W. Defined by James Watt in the 1780s. Used in the US and UK.
• Metric horsepower (PS / CV / pk): 735.49875 W. The dominant European unit. Listed on every German, French and Italian car.
• Brake horsepower (bhp): mechanical hp measured at the engine output shaft, after losses. In practice ≈ mechanical hp.

The exact conversion formulas

• hp = kW × 1.34102 — try kW to HP converter.
• kW = hp × 0.7457 — quick HP to kW.
• PS = kW × 1.35962 (metric horsepower).
• PS = hp × 1.01387 (so PS values are ~1.4% higher than hp).

Real-world car examples

Why the EU prefers kW

Since the 1970s the European Union has mandated kW as the legal unit on type-approval documents. Manufacturers may also display PS or hp, but kW is the official figure on registration certificates. This matters because insurance premiums and engine taxes are calculated from the kW figure in many EU countries. When importing a US car, the registered kW value will determine your insurance bracket.

A short history of horsepower

James Watt invented "horsepower" as a marketing tool. To convince mine owners to switch from real horses to his steam engines, he calculated that an average pit pony could lift 33,000 ft·lb in one minute. That number — converted to SI — became 745.7 watts and is still the definition of mechanical horsepower today. Two centuries later, every Mustang and Ferrari ad still quotes a ratio that originated in 18th-century coal pits.

Power vs torque: don't confuse them

Power tells you how fast you can do work; torque tells you the rotational force at a given moment. They are linked by engine speed: power (kW) = torque (Nm) × rpm ÷ 9,549. A diesel makes huge torque at low rpm; a high-revving petrol or electric motor delivers more power overall. Both numbers matter, but they describe different driving sensations.

EVs and the kW revolution

Electric cars have made kW intuitive again — partly because batteries are also rated in kWh (energy), so the units feel native. A 200 kW EV motor can sustain that 200 kW continuously, while a 200 kW (270 hp) ICE engine only briefly hits peak power. This is why an EV with similar peak hp often feels much faster off the line.

Quick mental conversion

• To go from kW to hp, multiply by 1.34. (100 kW ≈ 134 hp.)
• To go from hp to kW, multiply by 0.75. (200 hp ≈ 150 kW.)
• PS ≈ hp + 1.4% — usually ignored in casual conversation.

Common mistakes drivers and importers make

• Mixing hp and PS in marketing copy. A "523 hp BMW M3" might actually be 530 PS — the same engine, different unit. Always check which one you are quoting.
• Comparing peak hp across ICE and EV. An EV sustains its peak; a combustion engine only hits it briefly. A 200 kW EV outdraws a 200 kW petrol car at the lights.
• Using kW for tax filing in Europe. Insurance and engine tax brackets are calculated from the registered kW, not the marketing hp number — round down at your peril.
• Confusing kW and kWh. kW is power (rate); kWh is energy (total). A 200 kW motor draws 200 kWh per hour at full load.

Frequently asked questions

For exact answers and a printable table, use the Power converter.