What is Horsepower to Kilowatts Power Converter?
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Horsepower to Kilowatts Converter
1 mechanical HP = 0.7457 kW. Used for engine power, motors, electric vehicles.
About this converter
Horsepower (hp) is a non-SI unit of power. Mechanical (imperial) horsepower equals exactly 745.6998715823 watts, while metric horsepower (PS / ch / cv) equals exactly 735.49875 watts. The kilowatt (kW) is the SI unit of power (1 kW = 1,000 J/s). Which hp variant a spec sheet uses changes the answer by ~1.4 percent.
How it works
The two horsepower variants come from different historical mechanical definitions:
Mechanical HP = 33,000 ft*lbf/min
= 550 ft*lbf/s
= 745.6998715823 W
= 0.7456998716 kW (NIST SP 811)
Metric HP (PS) = 75 kgf*m/s
= 75 x 9.80665 W
= 735.49875 W
= 0.73549875 kW (ISO 80000-4)
1 kW = 1.34102 mechanical hp
= 1.35962 metric PS
For US, UK, and Australian car spec sheets use the mechanical factor (0.7457). For German, French, Italian, Japanese, and Korean spec sheets (and most European Union homologation documents) use the metric factor (0.7355).
Worked example
A BMW M3 brochure lists "510 PS" (German metric) but the US press kit lists "503 hp" (mechanical). Same engine. Sanity-check both numbers in kW:
- Convert PS: 510 x 0.73549875 = 375.10 kW.
- Convert mechanical hp: 503 x 0.7456998716 = 375.09 kW.
- Both round to 375 kW, so the spec sheets agree on actual power output. The 7 hp difference is purely a unit-conversion artefact.
- To round-trip 375 kW back to mechanical hp: 375 / 0.7457 = 503.0 hp.
Reference table
| hp (mech) | kW | PS (metric) | Typical machine |
|---|---|---|---|
| 1 | 0.7457 | 1.014 | One real working draft horse (peak) |
| 5 | 3.728 | 5.069 | Walk-behind lawn mower |
| 100 | 74.57 | 101.4 | Small economy car |
| 200 | 149.1 | 202.8 | Mid-sized family sedan |
| 503 | 375.0 | 510 | BMW M3 Competition (2024) |
| 670 | 500 | 679 | Ferrari 296 GTB |
| 1,020 | 761 | 1,034 | Tesla Model S Plaid (peak) |
| 1,500 | 1,119 | 1,521 | Bugatti Chiron Super Sport |
Common pitfalls
- Mechanical hp vs metric PS. 1 mechanical hp = 745.7 W; 1 metric PS = 735.5 W. The 1.4 percent gap is why a "510 PS" European spec converts to "503 hp" on US paperwork even though the engine is identical. Manufacturers selling globally will pick whichever number rounds better.
- Brake hp vs wheel hp. SAE J1349 brake hp (bhp) is measured at the engine flywheel with accessories disconnected. Wheel hp (whp) is at the road wheels and is typically 12 to 20 percent lower because of drivetrain losses. Comparing a flywheel-hp brochure number to a dyno-day whp number creates a false 15 percent shortfall.
- Electric "peak" vs "continuous" hp. EV motors can sustain peak output only for tens of seconds before thermal limits kick in. A "500 kW peak / 200 kW continuous" motor cannot deliver 500 kW for a full 1/4 mile, let alone a sustained track lap.
- Horsepower and torque are not the same thing. Power = torque x rpm / 5,252 (in mechanical hp and lb*ft). A 600 lb*ft diesel at 1,500 rpm makes only ~171 hp. A 200 lb*ft motorcycle engine at 11,000 rpm makes ~419 hp. Compare hp at the rpm where it peaks, not just the headline number.
- "1 hp" is not what 1 horse does. Real horses sustain 0.5 to 0.75 hp continuously; trained sprint horses can briefly hit 14 to 15 hp. Watt's 33,000 ft*lbf/min was a steam-engine marketing benchmark, not a biological measurement.
Related tools and references
Frequently asked questions
What is the exact horsepower to kilowatt factor?
Mechanical (imperial) horsepower is defined as exactly 33,000 ft*lbf/min, which equals 745.6998715822702 W. So 1 hp = 0.7456998716 kW. Metric horsepower (PS, ch, cv) is defined as 75 kgf*m/s = exactly 735.49875 W = 0.73549875 kW. Always check which definition a spec sheet uses.
What is the difference between mechanical HP and metric HP (PS)?
Mechanical HP (imperial) = 745.6999 W; used in the US and UK on most spec sheets. Metric HP (PS in Germany, ch in France, cv in Italy/Spain) = 735.4988 W; standard across continental Europe and Japan. The two differ by 1.4 percent: a car rated 200 PS is 197 mechanical hp.
What is brake horsepower (bhp) versus wheel horsepower (whp)?
Brake horsepower (bhp, SAE J1349) measures engine output at the flywheel, after accessories but before the transmission. Wheel horsepower (whp) is measured at the drive wheels on a chassis dynamometer and is typically 12 to 20 percent lower due to drivetrain friction. A 300 bhp engine usually puts ~245 whp at the wheels.
Where does the horsepower unit come from?
James Watt coined hp in 1782 to sell steam engines by comparing them to draft horses pumping water out of mines. He measured a horse turning a 12-foot mill wheel and derived 33,000 ft*lbf/min. Real horses can sustain only about 0.5 to 0.75 hp continuously, but can briefly peak above 14 hp in short sprints.
Sources
- NIST Special Publication 811 (2008) Guide for the Use of the International System of Units, Appendix B.8.
- ISO 80000-4:2019 Quantities and units - Part 4: Mechanics, definition of metric horsepower.
- SAE International (2004) J1349 Engine Power Test Code, brake horsepower reference conditions.
- BIPM (2019) The International System of Units (SI), 9th edition.