Power converter
Convert between watts, kilowatts, mechanical horsepower, metric horsepower (PS) and BTU per hour. Two horsepowers, 1.4% apart.
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Every power unit, one page
Pick any two units above. The conversions people look up most often have dedicated pages with reference tables, linked below.
The factors
| Unit | Watts | Note |
|---|---|---|
| Watt | 1 | SI — one joule per second |
| Kilowatt | 1000 | |
| Megawatt | 1,000,000 | |
| Mechanical horsepower | 745.6998716 | 550 ft·lbf/s |
| Metric horsepower (PS) | 735.49875 | 75 kgf·m/s, exact |
| BTU per hour | 0.2930710702 | |
| Kilocalorie per hour | 1.1622222 |
There are two horsepowers
They are 1.4% apart, and which one a figure uses depends on where it was published:
| Watts | Used in | |
|---|---|---|
| Mechanical horsepower (hp, bhp) | 745.70 | UK, US |
| Metric horsepower (PS, cv, pk, hk) | 735.50 | Germany, Japan, Korea, Taiwan, most of Europe |
A car advertised at 200 PS is 197.3 hp. Both figures describe the same engine, and manufacturers quote whichever their market expects — which is why the same model appears with two different power figures in two magazines.
PS stands for Pferdestärke. The same unit is cv in France and Italy, pk in the
Netherlands, and 匹 or 馬力 in Chinese. All of them are 735.49875 W.
See PS to hp.
BTU per hour is a power, not an energy
Air conditioners and heaters are rated in BTU per hour, and the “per hour” is routinely dropped in advertising, which makes a power look like an energy:
| Cooling capacity | BTU/h | kW |
|---|---|---|
| Small room | 5000 | 1.47 |
| Medium room | 9000 | 2.64 |
| Large room | 12,000 | 3.52 |
| Open-plan | 18,000 | 5.28 |
| Whole floor | 24,000 | 7.03 |
12,000 BTU/h is one “ton” of refrigeration — originally the cooling a ton of ice provides as it melts over a day — and it is 3.517 kW. That is why air conditioners are sized in tons in some markets and kilowatts in others.
Note that this is cooling output, not electricity consumed. A unit producing 3.52 kW of cooling might draw 1.1 kW from the wall, and the ratio between them is its efficiency.
Power is not energy
The most common confusion in this category, and it is not a conversion problem:
| Measures | Unit | |
|---|---|---|
| Power | rate | watt, kW, hp |
| Energy | amount | joule, kWh |
A 2 kW heater running for 3 hours uses 6 kWh. The kW is how fast, the kWh is how much, and an electricity bill charges for the second. See the energy converter.
Reference powers
| Watts | hp | |
|---|---|---|
| LED bulb | 10 | 0.013 |
| Laptop | 60 | 0.080 |
| Human, sustained cycling | 200 | 0.27 |
| Microwave oven | 1000 | 1.34 |
| Electric kettle | 2500 | 3.35 |
| Home EV charger | 7000 | 9.4 |
| Small car engine | 75,000 | 100 |
| Rapid EV charger | 150,000 | 201 |
| Wind turbine | 3,000,000 | 4023 |
Where people go wrong
bhp and hp are the same unit. “Brake horsepower” describes how the measurement was taken — at the flywheel, on a brake dynamometer — not a different size of horsepower.
A kilowatt-hour is not a unit of power, despite containing one. It is energy, and it belongs to the energy converter.