How this calculator works
This converter covers watts and their metric multiples alongside two distinct horsepower units and BTU per hour. Power specifications on vehicles and machinery are a common source of confusion because 'horsepower' is not one single unit worldwide.
Mechanical horsepower (also called imperial horsepower), used in the US and UK, is defined as exactly 550 foot-pounds-force per second, equal to 745.6998715822702 W. Metric horsepower (PS in German, CV in French and Spanish, pk in Dutch), used across most of continental Europe and Japan, is defined as exactly 75 kilogram-force-meters per second, equal to 735.49875 W. The two differ by about 1.4%, small enough to ignore casually but large enough to matter when comparing published specifications from different regions.
How it converts
result = value × (watts per from-unit) ÷ (watts per to-unit)Exact anchors: 1 hp (mechanical) = 745.6998715822702 W · 1 hp (metric) = 735.49875 W · 1 BTU/h = 1,055.05585262 ÷ 3,600 WWorked example: 150 hp (mechanical) to kilowatts
- Mechanical horsepower is defined as 745.6998715822702 W per hp.
- 150 hp × 745.6998715822702 W/hp = 111,854.98 W.
- 111,854.98 W ÷ 1,000 = 111.85 kW.
Frequently asked questions
What is the difference between mechanical and metric horsepower?
Mechanical (imperial) horsepower is 745.6998715822702 W, based on 550 foot-pounds-force per second. Metric horsepower (PS/CV/pk) is 735.49875 W, based on 75 kilogram-force-meters per second. A car rated 'PS' has a slightly lower wattage than the same number of mechanical horsepower.
Why do European car brochures list PS instead of hp?
PS (Pferdestärke, German for horsepower) is the metric horsepower unit historically used across continental Europe. Modern brochures increasingly quote kilowatts directly, as required by EU regulation, alongside PS.
How is BTU per hour used?
BTU/h rates the power of heating and cooling equipment, such as air conditioners and furnaces, in the US. This calculator uses the International Table BTU (1,055.05585262 J) divided by 3,600 seconds to get watts per BTU/h.
Is power the same thing as energy?
No. Power is the rate energy is used or produced (watts = joules per second); energy is the total amount used over time (joules, or kilowatt-hours). To convert power to energy, multiply by a duration — see the energy converter for units like kWh and BTU.
How do I convert kilowatts to horsepower?
Divide the kilowatt figure by 0.7456998715822702 (the exact kW-per-mechanical-horsepower value), or multiply by about 1.341. Reversing this page's own worked example confirms it: 111.85 kW ÷ 0.7456998715822702 ≈ 150 hp, the same 150 hp the example started from.