Power converter for watts, horsepower and BTU/h
This power converter works with nine units: milliwatts through gigawatts, mechanical horsepower (hp), metric horsepower (PS), BTU per hour and foot-pounds per second. Power is a rate of energy use, one joule per second being one watt.
Two horsepowers
"Horsepower" has more than one definition, and this tool offers the two most common:
- Mechanical horsepower (hp): 550 foot-pounds per second, which is 745.69987158227 W. Used for US and UK engine ratings.
- Metric horsepower (PS, CV, pk): 75 kilogram-force meters per second, which is exactly 735.49875 W. Common on European and Asian car specifications.
One hp equals 1.013869665 PS, so the metric figure for the same engine is about 1.4% higher. A 100 kW engine is 134.102209 hp or 135.9621617 PS. Motor nameplates sometimes use a third value, the electrical horsepower of exactly 746 W, which is within 0.05% of mechanical hp.
Examples
1 hp = 745.6998716 W
1 PS = 735.49875 W
7.5 kW = 10.05766567 hp
550 ftlbs = 745.6998716 W
12000 BTUh = 3.516852842 kW
3.5 kW = 11942.49572 BTUhTypical power ratings for scale
| Device or system | Approximate power |
|---|---|
| LED light bulb | 5–10 W |
| Laptop charger | 45–100 W |
| Microwave oven | 800–1,200 W |
| Electric kettle | 2–3 kW |
| Small car engine | ≈ 75 kW (about 100 hp) |
| Onshore wind turbine | 2–5 MW |
| Large power station unit | ≈ 1 GW |
Motor ratings need one extra step: the horsepower on a motor's nameplate is its mechanical output, not what it draws from the supply. A 1 hp motor that is 85% efficient takes about 745.7 ÷ 0.85 ≈ 877 W of electrical power, which is the figure to use when sizing a circuit or generator.
BTU per hour for heating and cooling
Air conditioners and heaters are often rated in BTU per hour. One BTU/h is 0.29307107017 W. The HVAC "ton of refrigeration" is 12,000 BTU/h, about 3.52 kW of cooling. When comparing a unit rated in BTU/h with one in kW, convert both to the same unit before looking at price or efficiency.
Power versus energy
Watts measure how fast energy is used; watt-hours measure how much. A 2 kW kettle running for 3 minutes uses 0.1 kWh. For amounts of energy, use the energy converter. For electrical circuits, power equals voltage times current, so a 2300 W load on a 230 V supply draws 10 A; the electric current converter switches between amperes and milliamperes.
Common mistakes
- Assuming the horsepower in a European brochure is mechanical hp; it is usually PS.
- Reading an air conditioner's "BTU" as an amount of energy. On equipment ratings it nearly always means BTU per hour.
- Confusing mW (milliwatt) with MW (megawatt), which differ by a factor of a billion.