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 = 745.69987158227022 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 lists mechanical horsepower (hp) and metric horsepower (PS) as separate units; they 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
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience.
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 7 power units simultaneously, including metric horsepower (PS).
Common Conversions
| Watts (W) | Horsepower (hp) | BTU/h | Context |
|---|---|---|---|
| 1 W | 0.00134 hp | 3.41 BTU/h | One watt — small LED indicator light |
| 60 W | 0.0805 hp | 205 BTU/h | Traditional incandescent bulb |
| 745.7 W | 1.0 hp | 2,544 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 |