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Convert horsepower, brake horsepower, metric PS, kilowatts and BTU/h, with drivetrain loss and power-to-weight.
This converter moves a power figure between mechanical horsepower, metric PS, kilowatts, watts, BTU/h and related units using their exact definitions rather than rounded factors: mechanical horsepower is 550 ft·lbf/s = 745.6998716 W, metric horsepower is 75 kgf·m/s = 735.49875 W, and electrical horsepower is defined as exactly 746 W. It also separates crankshaft power from wheel power using a drivetrain-loss allowance, and reports power-to-weight in hp, kW and PS per tonne. Built for anyone comparing a German PS figure against a US horsepower figure, or a dyno printout against a manufacturer's claim.
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Uses 745.6998716 W and 735.49875 W rather than the rounded 746 and 735 that drift by a horsepower or more on big engines.
Metric PS reads about 1.4% higher than mechanical hp for the same engine, which is why the same car is quoted differently in different markets.
Applies a drivetrain loss so a dyno figure and a brochure figure can be compared like for like.
149.14 kW. One mechanical horsepower is exactly 745.6998716 watts, so 200 hp × 745.6998716 = 149,140 W. Going the other way, 100 kW is 134.10 hp.
PS is a genuinely different unit — metric horsepower, 75 kgf·m/s or 735.49875 W — so 200 hp equals 202.77 PS, about 1.4% higher. Bhp is not a different unit at all: it is mechanical horsepower measured at the crankshaft on a brake dynamometer, as opposed to wheel horsepower measured at the tyres.
Roughly 10-15% for front- and rear-wheel drive and 20-25% for all-wheel drive, with automatics at the higher end of each range. A 300 hp crank figure through a rear-drive manual therefore reads around 255 hp at the wheels. These are rules of thumb, not measured constants — actual loss varies with gearing, tyres, temperature and the dyno itself.
Only electrical horsepower is, by definition, and that unit is used on US electric motor nameplates. Mechanical horsepower — the one used for engines — is 550 ft·lbf/s, which works out to 745.6998716 W. The difference is about 0.04%, negligible on a small motor but worth a fraction of a horsepower on a 500 hp engine.
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