Power Converters
Power measures how fast energy is used or produced. Engines and motors are rated in horsepower, electrical equipment in watts and kilowatts, and heating and cooling gear in BTU per hour. The word "horsepower" alone hides two different units (mechanical and metric), which is the main trap when comparing a car or a machine from different countries. These converters use the exact definitions so you can compare engines, appliances and heating systems on the same scale.
All power converters
Things to know about power conversions
- There are two horsepowers: mechanical (745.7 W) and metric (735.5 W). Always check which one a car or machine specification uses before comparing.
- Kilowatts measure how fast energy is used; kilowatt-hours measure how much. A 2 kW heater running for 3 hours uses 6 kWh.
- Heating and cooling equipment is rated in BTU per hour, a unit of power. 3,412 BTU/h equals 1 kW.
Power conversion chart
Read across: one of the unit in the left column equals the value shown under each unit.
| 1 unit = | W | kW | MW | hp | PS | BTU/h |
|---|---|---|---|---|---|---|
| W | 1 | 0.001 | 1 × 10-6 | 0.001341 | 0.00136 | 3.412 |
| kW | 1,000 | 1 | 0.001 | 1.341 | 1.36 | 3,412 |
| MW | 1,000,000 | 1,000 | 1 | 1,341 | 1,360 | 3,412,142 |
| hp | 745.7 | 0.7457 | 0.0007457 | 1 | 1.014 | 2,544 |
| PS | 735.5 | 0.7355 | 0.0007355 | 0.9863 | 1 | 2,510 |
| BTU/h | 0.2931 | 0.0002931 | 2.931 × 10-7 | 0.000393 | 0.0003985 | 1 |
Power units explained
- Watt (W)
- The watt is the SI unit of power: one joule per second. A typical LED bulb uses 5 to 10 watts and a kettle around 2,000 watts.
- Kilowatt (kW)
- A kilowatt is 1,000 watts. It is the usual unit for engine output in Europe and for the power of electric motors, heaters and chargers.
- Megawatt (MW)
- A megawatt is one million watts. Power stations, wind farms and large industrial plants are rated in megawatts.
- Mechanical horsepower (hp)
- Mechanical (imperial) horsepower is about 745.7 watts. It is the figure behind the "hp" rating on US and UK cars, lawn mowers and motors.
- Metric horsepower (PS) (PS)
- Metric horsepower, written PS (Pferdestärke) or CV, is exactly 735.49875 watts. It is used on European and Japanese car specifications and is about 1.4 percent smaller than mechanical horsepower.
- BTU per hour (BTU/h)
- BTU per hour is the rate at which heat is moved. Air conditioners and furnaces are rated in it; 12,000 BTU/h is called one ton of cooling and is about 3.52 kilowatts.