Free Power Converter
Convert power units instantly — watts, kilowatts, megawatts, horsepower, BTU/hour, calories per second. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Power is energy per unit time, and the units reflect different eras of industrial history: 1 watt = 1 joule/second by definition, 1 mechanical horsepower = 745.699872 watts (based on James Watt's 18th-century estimate of a horse's sustained work rate), and 1 metric horsepower (PS) = 735.49875 watts — a slightly different value used across continental Europe and Japan. This converter distinguishes mechanical and metric horsepower, which differ by about 1.4%.
Practical Real-World Scenarios
- Automotive specifications: US car listings quote horsepower while European and Japanese manufacturers often use metric horsepower (PS or CV), producing slightly different numbers for equivalent engines.
- Electrical engineering: household and industrial electrical power is universally rated in watts or kilowatts on nameplates and utility bills worldwide.
- Renewable energy: solar panel and wind turbine output is rated in watts or kilowatts, requiring conversion when comparing to older horsepower-rated equipment.
Historical & Technical Background
James Watt coined 'horsepower' in the 1780s while marketing his steam engines, estimating it from observations of horses turning a mill — a figure since criticized as somewhat generous to the horse, but which stuck as a marketing and engineering convention. The watt, adopted as the SI unit of power in 1889 and named for Watt himself, is defined precisely in terms of joules and seconds, giving it a rigor the empirically-derived horsepower never had.
Precision & Accuracy Statement
Every conversion factor used on this page is checked against internationally recognized reference standards — BIPM SI Brochure definitions and NIST Special Publication 811 conversion factors — rather than approximated or rounded for display. Where a constant is fixed by international definition (such as 1 inch = 2.54 cm, or standard gravity = 9.80665 m/s²), we use the exact defined value. Where a figure is a practical industry convention rather than a physical constant, that distinction is stated explicitly above so results are never presented with false precision.
How This Converter Works
Power measures energy transfer rate. Watts are used in electronics and electricity, horsepower in engines, BTU/h in HVAC. Our converter handles all 6 power units simultaneously.
Common Conversions
| Watts (W) | Horsepower (hp) | BTU/h | Context |
|---|---|---|---|
| 1 W | 0.00134 hp | 3.41 BTU/h | One watt — LED light bulb |
| 60 W | 0.0805 hp | 205 BTU/h | Traditional incandescent bulb |
| 745.7 W | 1.0 hp | 2,545 BTU/h | One horsepower |
| 1,000 W | 1.341 hp | 3,412 BTU/h | One kilowatt — hair dryer |
| 150,000 W | 201 hp | 511,800 BTU/h | Average car engine |