UnitSnapPower converter
Power is the rate at which energy is transferred or converted. The SI unit is the watt (W), one joule per second. Milliwatts describe electronics and lasers, kilowatts describe appliances, vehicle engines, and solar systems, and megawatts describe power plants and large industrial equipment.
Convert between 8 power units. Pick any two units below; results update as you type.
Popular power conversions
About power units
Engine output is often given in horsepower, but two versions exist. Mechanical horsepower, common in the US and UK, is exactly 550 foot-pounds-force per second, about 745.7 W. Metric horsepower (PS or CV), common in continental Europe, is 75 kilogram-force meters per second, about 735.5 W. Air conditioners and heaters in the US are rated in BTU per hour.
The horsepower was introduced by James Watt in the late 18th century to compare steam engines with draft horses, and the SI unit of power was later named after him.
Tips
- Mechanical and metric horsepower differ by about 1.4%, so check which one a car specification uses.
- A kilowatt is roughly 1.34 mechanical horsepower, a quick estimate for comparing engine ratings.
- Power is a rate, not an amount: multiply watts by hours to get energy in watt-hours.
All power units
| Unit | Symbol | Value in watts |
|---|---|---|
| Watts | W | 1 W = 1 W |
| Milliwatts | mW | 1 mW = 0.001 W |
| Kilowatts | kW | 1 kW = 1,000 W |
| Megawatts | MW | 1 MW = 1,000,000 W |
| Mechanical Horsepower | hp | 1 hp = 745.6999 W |
| Metric Horsepower | PS | 1 PS = 735.4988 W |
| BTUs per Hour | BTU/h | 1 BTU/h = 0.2930711 W |
| Foot-Pounds per Second | ft·lbf/s | 1 ft·lbf/s = 1.355818 W |
Convert offline on your phone. 36 categories, live currency rates, calculators and history in our free Unit Converter app.
Factors: NIST SP 811 · SI Brochure · NIST Handbook 44 — Updated