Power converter
Convert watts, kilowatts and horsepower — with mechanical hp and metric PS kept apart, because the same engine is quoted as both.
Common power conversions
Every power unit
| Unit | Symbol | In watts |
|---|---|---|
| Watts | W | 1 |
| Kilowatts | kW | 1,000 |
| Megawatts | MW | 1,000,000 |
| Mechanical horsepower | hp | 745.699872 |
| Metric horsepower | PS | 735.49875 |
| BTU per hour | BTU/h | 0.29307107 |
| Foot-pounds per second | ft·lbf/s | 1.355818 |
Questions
Why does the same car have two different horsepower figures?
Because there are two horsepowers. Metric horsepower, written PS or CV, is 735.49875 W; mechanical horsepower, written hp or bhp, is about 745.7 W. A car sold as 150 PS in Germany is 148 hp in Britain, and nothing about the engine has changed.
Where does 746 watts come from?
From James Watt, who needed to sell steam engines to people who owned horses. He measured a mill horse turning a wheel and settled on 550 foot-pounds per second — a figure most real horses cannot sustain, which made the comparison flattering to his engines.
How do I read an air conditioner's BTU rating?
BTU ratings are BTU per hour, a rate of heat movement, even when the "per hour" is dropped. A 12,000 BTU/h unit shifts about 3.5 kW of heat. That is not what it draws from the wall — a decent unit moves several times more heat than the electricity it consumes.
What is the difference between power and energy?
Power is a rate, energy is an amount. A kilowatt is how fast something uses energy; a kilowatt-hour is how much it used. A 2 kW heater running for three hours has a power of 2 kW throughout and has consumed 6 kWh. Bills are in energy; ratings are in power.