hp vs bhp vs PS vs kW

A car sold as 300 bhp in Britain is 304 PS in Germany and 224 kW on its own registration document. Nothing about the engine differs. Three numbers, three conventions, one machine — and the gaps are big enough to matter when comparing cars across markets.

Every Unit at a Glance

Notice that PS, KM, KS, cv, pk and hk are all the same unit with different names — exactly 75 kilogram-force metres per second. Only mechanical horsepower and the kilowatt are genuinely different quantities.

hp vs bhp — Is There Actually a Difference?

Numerically, no. Both are 745.7 watts. The distinction is about where and how the measurement was taken.

• Brake horsepower (bhp) is measured at the crankshaft on an engine dyno, using a brake to apply load. The engine is typically on a stand.
• Horsepower (hp) is used loosely for either crank or wheel figures, which is exactly why confusion arises.
• Wheel horsepower (whp) is measured at the wheels on a chassis dyno, so it is 12–25% lower depending on drivetrain.

In British usage bhp almost always means the manufacturer's crank figure. In American usage "hp" usually means the same thing, quoted to the SAE net standard. The unit is identical; only the measuring point differs. Our guide to wheel HP vs crank HP covers that gap.

PS, KM and KS — the Metric Family

Metric horsepower was defined to be a round number in metric terms: the power needed to lift 75 kilograms by one metre in one second. That works out to 735.49875 watts, slightly less than the imperial definition of 550 foot-pounds per second.

The practical consequence is that a car always has a higher PS number than hp number. Some quick reference points:

Round numbers in one system look odd in the other, which is a useful clue. A car advertised as exactly 150 PS or 204 PS was specified in metric horsepower; one advertised as exactly 200 bhp or 300 bhp was specified in imperial.

How to Spot Which Unit You Are Reading

1. Check the registration document. EU papers must state kilowatts, so that figure is unambiguous.
2. Look for suspiciously round numbers. 110 kW, 150 PS and 148 bhp are the same car — whichever is roundest is probably the original.
3. Note the source country. German, French, Italian and Japanese material almost always quotes metric horsepower even when it writes "hp".
4. Watch for badge numbers. Many model names encode kW or PS rather than either horsepower.

The Bigger Variable: Test Standards

Unit choice causes a 1.4% discrepancy. Test standards have historically caused far larger ones.

American figures before 1972 were quoted as SAE gross — engine on a stand with no alternator, water pump, air cleaner or exhaust system fitted. The switch to SAE net, measured with all accessories installed, made identical engines appear to lose 20–30% overnight. This is why classic muscle car figures look so inflated against modern equivalents.

Modern standards such as SAE J1349 and the European ECE R85 measure comparably, so contemporary figures across markets are broadly trustworthy once the unit is accounted for. Our SAE horsepower calculator covers correction factors.

Converting Between Them

The factors, all exact:

Use our kW to PS converter for the metric scale, kW to HP for mechanical, or the horsepower unit converter to see every unit at once. The full derivation is in the exact HP to kW conversion.