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Power Converter

Convert power between watts, kilowatts, megawatts, milliwatts, mechanical and metric horsepower, BTU per hour, tons of refrigeration, ft·lbf/s, cal/s and kcal/h.

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Convert an amount of power

Read the guide How to Convert Horsepower to Kilowatts (and Other Power Units)

How to use the converter

Type an amount in the Value box, choose the unit you have and the unit you want, and press Convert. The swap button flips the two units, and a table below the result shows the same power in all eleven units. The converter starts on horsepower to kilowatts.

Unit definitions

Power is the rate at which energy is used or delivered. Every unit is converted through the watt (W), which is one joule per second. The factors used are:

  • Milliwatt (mW) = 0.001 W, kilowatt (kW) = 1,000 W and megawatt (MW) = 1,000,000 W.
  • Horsepower (hp), the mechanical or imperial horsepower, is 550 foot-pounds force per second, which is 745.69987158227022 W. It is the unit used for engines in the United States and the United Kingdom.
  • Metric horsepower (PS) is 75 kilogram-force meters per second, exactly 735.49875 W. It is also written CV or ch and is common for cars in Europe. It is about 1.4% smaller than the mechanical horsepower.
  • BTU per hour (BTU/h) uses the International Table BTU of 1,055.05585262 J, so 1 BTU/h ≈ 0.293071 W. Heaters and air conditioners are often rated in BTU/h.
  • Ton of refrigeration (TR) = 12,000 BTU/h = 3,516.8528420667 W. It comes from the cooling power of melting one short ton of ice in a day.
  • Foot-pound force per second (ft·lbf/s) = 1.3558179483314004 W.
  • Calorie per second (cal/s) = 4.184 W, using the thermochemical calorie, and kilocalorie per hour (kcal/h) = 4,184 ÷ 3,600 ≈ 1.162222 W.

To convert, multiply by the factor of the starting unit and divide by the factor of the target unit.

Worked examples

  • 1 hp to kW: 745.69987 W ÷ 1,000 ≈ 0.7457 kW.
  • 100 kW to hp: 100,000 ÷ 745.69987 ≈ 134.10 hp. An electric car motor rated at 100 kW is roughly a 134 hp engine.
  • 1 hp to metric hp: 745.69987 ÷ 735.49875 ≈ 1.01387 PS.
  • 1 ton of refrigeration to kW: 3,516.85 W ÷ 1,000 ≈ 3.52 kW, which is the cooling output of a typical 12,000 BTU/h air conditioner.
  • 1 kW to BTU/h: 1,000 ÷ 0.293071 ≈ 3,412.14 BTU/h.

Good to know

  • Do not confuse power with energy. A kilowatt (kW) is power; a kilowatt-hour (kWh) is energy, the amount used by 1 kW running for one hour. Use an energy converter for kWh, joules or calories.
  • Other horsepower definitions exist, such as electrical horsepower (746 W) and boiler horsepower (about 9,810 W). This converter uses the mechanical and metric versions, the two used for engines.
  • Results show up to six decimal places; very small values are written in scientific notation.
  • Power cannot be negative here. Zero is accepted.

Frequently asked questions

How many kilowatts is one horsepower?

One mechanical horsepower is about 0.7457 kW (745.7 W). One metric horsepower (PS) is about 0.7355 kW (735.5 W).

What is the difference between hp and PS?

Both are called horsepower. The mechanical horsepower (hp) is 550 ft·lbf per second, about 745.7 W. The metric horsepower (PS, CV or ch) is 75 kgf·m per second, exactly 735.49875 W. One hp equals about 1.014 PS.

How many watts is a 12,000 BTU air conditioner?

A 12,000 BTU/h rating is a cooling output of about 3,517 W, which is also one ton of refrigeration. The electrical power it draws is lower, because air conditioners move more heat than the energy they use.

Is a kilowatt the same as a kilowatt-hour?

No. A kilowatt measures power, the rate of energy use. A kilowatt-hour measures energy: 1 kW used for one hour is 1 kWh.