What the power converter does
Power is the rate at which energy is used or delivered, and this converter switches it between watts, kilowatts, megawatts, horsepower and BTU per hour. Enter a number, choose the two units and press Convert. The value goes through the watt, the SI unit of power, and the result is displayed to up to 8 decimal places.
Conversion factors
| Unit | Symbol | In watts |
|---|---|---|
| Watt | W | 1 |
| Kilowatt | kW | 1,000 |
| Megawatt | MW | 1,000,000 |
| Horsepower (mechanical) | hp | 745.6998715822702 |
| BTU per hour | BTU/h | 0.293071070172 |
A watt is one joule per second, per the BIPM SI Brochure.
The horsepower here is the mechanical (imperial) horsepower that James Watt set at 550 foot-pounds-force per second. Built from the exact foot (0.3048 m) and pound-force (4.4482216152605 N), it comes to 550 × 0.3048 × 4.4482216152605 = 745.6998715822702 W.
BTU per hour is the International Table BTU (1,055.05585262 J) divided by 3,600 seconds, which is 0.2930710701722… W. The converter stores it to 12 decimal places, 0.293071070172, so its kW to BTU/h result (3,412.14163313) matches the energy converter's kWh to BTU.
Which horsepower?
"Horsepower" means different things depending on where the number came from. Only the first one is in this converter.
| Name | Watts | Where you'll see it |
|---|---|---|
| Mechanical horsepower (hp) | 745.69987… | US and UK engine and motor ratings |
| Metric horsepower (PS, CV) | 735.49875 | European and Japanese car specs |
| Electrical horsepower | 746 | Some electric motor nameplates |
Entering 746 W gives 1.0004 hp, which shows how close the electrical figure is to the mechanical one. A car listed at 150 PS is 150 × 0.73549875 = 110.3 kW, while 150 hp is 111.85 kW. NIST Special Publication 811 lists the different horsepower definitions.
Quick reference
| From | To | Multiply by |
|---|---|---|
| hp | kW | 0.745700 |
| kW | hp | 1.34102 |
| kW | BTU/h | 3,412.14 |
| BTU/h | W | 0.293071 |
| MW | hp | 1,341.02 |
Worked examples
- A 200 hp car engine in kilowatts: 200 × 0.7457 = 149.14 kW.
- A 12,000 BTU/h air conditioner in watts: 12,000 × 0.293071070172 = 3,516.85 W.
- A 24,000 BTU/h (two-ton) system: 7.03 kW.
- A 3.5 kW electric heater in BTU/h: 3.5 × 3,412.14 = 11,942.5 BTU/h.
- A 1 MW wind turbine in horsepower: 1,341.02 hp.
Power ratings vs electricity use
An air conditioner's BTU/h figure is the heat it moves, not the power it draws from the wall. A 3.5 kW (12,000 BTU/h) unit commonly draws around a third of that in electricity, because heat pumps move more heat than the electrical energy they consume. Check the electrical input on the nameplate before sizing a circuit or estimating a bill. To turn a power draw into energy, multiply by hours of use and convert the kWh in the energy converter.
Related converters and calculators
- Energy converter: joules, kWh, calories and BTU.
- Force converter: newtons, pound-force and kilogram-force.
- Fuel cost calculator: what a trip costs from distance, mileage and fuel price.
- Temperature converter: Celsius, Fahrenheit and Kelvin.
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