Power Converter
Watts, kilowatts and horsepower.
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Result
0.7456998716 kW
1 horsepower (mechanical) in kilowatt
1 hp = 0.7456998716 kW
Power Conversion Math Formula
Power is energy per unit of time, so every power unit is a rate. One watt is one joule per second. That means a watt cannot be turned into an energy unit without also saying for how long. What this tool does is convert one rate into another, passing through watts.
Horsepower is where it gets interesting. James Watt defined it as 33,000 foot-pounds of work per minute, which is 550 foot-pounds per second. In watts that is 550 × 1.3558179 = 745.7 W, the mechanical horsepower. The metric horsepower (PS or CV) is defined as lifting 75 kilograms by 1 metre in 1 second, which is 735.5 W. They are two different units that share a name.
The formula
value in B = value in A × (W per A) ÷ (W per B)1 hp = 745.69987158 W, 1 PS = 735.49875 W, 1 BTU/h = 0.29307107 WEnergy = Power × Time
Worked example 1: A 150 hp engine, in kilowatts
150 hp × (745.69987158 W ÷ 1 hp) = 111,854.98 W111,854.98 W × (1 kW ÷ 1,000 W)Answer: 111.855 kW
The kilowatt is the figure used for electric motors and for most car specifications outside the US.
Worked example 2: 100 kW, in metric horsepower
100 kW × (1,000 W ÷ 1 kW) = 100,000 W100,000 W × (1 PS ÷ 735.49875 W)Answer: 135.962 PS
With the mechanical horsepower you would get 134.1 hp instead, about 1.4% fewer, because the mechanical horsepower is the larger unit.
Worked example 3: 12,000 BTU/h, in watts
12,000 BTU/h × (0.29307107 W ÷ 1 BTU/h)Answer: 3,516.85 W
12,000 BTU/h is called one ton of refrigeration in air conditioning. It is roughly 3.5 kW of cooling.
Common mistakes to avoid
- Mixing the two horsepowers. Mechanical horsepower is 745.7 W and metric horsepower is 735.5 W, a gap of about 1.4%. A car rated at 300 PS makes 220.6 kW, while 300 hp is 223.7 kW. Check which one a datasheet means.
- Treating power as energy. A 3 kW heater does not use 3 kW. It draws 3 kW while it is on. Run it for 2 hours and it has used 3 kW × 2 h = 6 kWh of energy. Power is how fast, energy is how much.
- BTU against BTU per hour. A BTU is an amount of energy (about 1,055 J). A BTU/h is power (about 0.293 W). Air conditioner and boiler ratings given in BTU almost always mean BTU per hour.
About power units
Power measures how quickly energy is used or delivered. The SI unit is the watt, one joule per second. Household devices are quoted in watts, power stations in megawatts, car and motorbike engines in kilowatts or horsepower, and heating and cooling equipment in BTU per hour.
Horsepower has more than one definition. This tool uses the mechanical (imperial) horsepower, 745.7 W, and the metric horsepower, PS, from the German Pferdestärke, at 735.5 W. On a datasheet, PS or CV means the metric one, and hp is usually the mechanical one in the US.
- Watt (W)One joule per second. The SI unit.
- Kilowatt (kW)1 kW = 1,000 WA thousand watts. The usual rating for motors and appliances.
- Megawatt (MW)1 MW = 1,000,000 WA million watts. Power plants and large industrial sites.
- Horsepower (mechanical) (hp)1 hp = 745.6998716 W550 foot-pounds per second. The horsepower on US car specifications.
- Horsepower (metric) (PS)1 PS = 735.49875 W75 kilogram-force metres per second. Written PS or CV in Europe.
- BTU per hour (BTU/h)1 BTU/h = 0.29307107 WThe rating unit for heaters and air conditioners.
Power conversion table
| Value | W | kW | hp | PS |
|---|---|---|---|---|
| 1 W | 1 | 0.001 | 0.00134102 | 0.00135962 |
| 1 kW | 1,000 | 1 | 1.34102 | 1.35962 |
| 1 MW | 1,000,000 | 1,000 | 1,341.02 | 1,359.62 |
| 1 hp | 745.7 | 0.7457 | 1 | 1.01387 |
| 1 PS | 735.499 | 0.735499 | 0.98632 | 1 |
| 1 BTU/h | 0.293071 | 0.000293071 | 0.000393015 | 0.000398466 |
Power converter FAQ
How do I convert horsepower to kilowatts?
Multiply by 0.7457. A 200 hp engine is 200 × 0.7457 = 149.1 kW.
How do I convert kilowatts to horsepower?
Multiply by 1.341. 75 kW × 1.34102 = 100.6 hp.
What is the difference between hp and PS?
Mechanical horsepower is 745.7 W and metric horsepower (PS) is 735.5 W. A car rated at 300 PS makes 220.6 kW, while 300 hp is 223.7 kW, a difference of about 1.4%.
How many watts is one BTU per hour?
0.293071 W. A 10,000 BTU/h heater is about 2,931 W, or 2.93 kW.
What is the difference between a watt and a watt-hour?
A watt is power and a watt-hour is energy. A 100 W lamp uses 100 Wh for every hour it stays lit.
How many watts is one horsepower?
745.7 W for a mechanical horsepower, so a 1 hp motor with perfect efficiency would draw 745.7 W. Real motors lose some energy as heat, so a 1 hp motor draws more than that from the wall.