Power Converter

How to use the power converter

Choose the unit you have in From and the unit you want in To, type the value and press Convert. Negative values are accepted; the questions at the end of the page explain why.

How power conversion works

Power is the rate at which energy is transferred. Its SI unit is the watt (W), one joule per second, and every unit in this converter is a fixed multiple of it. The converter changes your value to watts and then to the target unit. The main definitions are:

• Mechanical horsepower (hp): 550 foot-pounds force per second, about 745.70 W.
• Metric horsepower (PS): 75 kilogram-force meters per second, exactly 735.49875 W.
• Electric horsepower (hp (E)): exactly 746 W by definition.
• Btu per hour: one International Table Btu per hour, about 0.293071 W.
• Ton of refrigeration (TR): exactly 12,000 Btu/h, about 3.5169 kW.
• Kilocalorie per hour: one International Table kilocalorie per hour, exactly 1.163 W.

Common power conversion factors

Multiply a value in the first unit by the factor to get the second unit.

Worked examples

• 150 kW engine to horsepower: 150 × 1.341022 ≈ 201.15 hp, or 150 × 1.359622 ≈ 203.94 PS.
• 100 hp to kW: 100 × 0.7457 ≈ 74.57 kW.
• An air conditioner rated 12,000 Btu/h: 12,000 × 0.293071 ≈ 3.52 kW of cooling, exactly 1 TR.
• A 2.5 TR chiller to kW: 2.5 × 3.516853 ≈ 8.79 kW.

Kilowatts to horsepower

Horsepower to kilowatts

Btu per hour to kilowatts and tons of refrigeration

Three different horsepowers

"Horsepower" names several units of slightly different size, and specifications do not always say which one they mean.

• Mechanical horsepower (hp) is the imperial unit of 550 ft·lbf/s, the one usually meant by "hp" in the United States and the United Kingdom.
• Metric horsepower (PS), from the German Pferdestärke, is also written CV or ch in other languages. It is about 1.37% smaller than mechanical horsepower: a 300 PS engine is 220.65 kW, which is about 295.9 hp.
• Electric horsepower is a round 746 W, very close to mechanical horsepower.

Terms such as "brake horsepower" describe where the power was measured, at the engine's output shaft, rather than a different unit size. When a figure matters, the kilowatt value removes the ambiguity.

Btu/h and tons of refrigeration in HVAC

Heating and cooling equipment is often rated in Btu per hour, and larger cooling systems in tons of refrigeration. An air conditioner advertised as "12,000 BTU" means 12,000 Btu/h, a power, not an amount of energy. The ton comes from the heat needed to melt one short ton (2,000 lb) of ice in 24 hours: with the traditional latent heat of 144 Btu per pound, 144 × 2,000 ÷ 24 = 12,000 Btu/h.

These ratings describe the heat moved, not the electricity drawn. A heat pump or air conditioner usually moves more heat than the electrical power it consumes; the ratio is its coefficient of performance (COP) when both are in the same unit, or its energy efficiency ratio (EER) when cooling is in Btu/h and input in watts. Do not size a circuit from a cooling rating converted to kW.

Common pitfalls

• Power is not energy. A 3 kW heater uses 3 kWh only if it runs at full power for one hour. To convert kWh or joules, use the energy converter.
• kVA is not kW. Generators and transformers are often rated in kilovolt-amperes, which is apparent power. Real power in kW is kVA multiplied by the power factor, so kVA is not offered here.
• Btu and Btu/h are different. Btu measures energy and Btu/h measures power; labels often drop the "/h".

Frequently asked questions

How many watts are in one horsepower?

About 745.70 W for mechanical horsepower, exactly 735.49875 W for metric horsepower (PS) and exactly 746 W for electric horsepower.

How do I convert kW to hp?

Multiply by about 1.341022 for mechanical horsepower, or by about 1.359622 for PS.

How many kW is one ton of refrigeration?

About 3.5169 kW, since one ton is exactly 12,000 Btu/h.

How many Btu/h is 1 kW?

About 3,412.14 Btu/h, so 5 kW is about 17,060.71 Btu/h.

How do I work out the energy a device uses from its power?

Multiply the power by the running time. A device drawing 1,500 W for 2 hours uses 1.5 kW × 2 h = 3 kWh. Convert the power to kW first if it is given in another unit, such as horsepower.

Why does the converter accept negative power?

A sign is often used to show the direction of power flow, for example whether a battery is charging or discharging, or whether a home is importing from or exporting to the grid. Which direction counts as negative depends on the convention in use. The sign stays the same in every unit, because each unit is a positive multiple of the watt.

Supported units

• Watt (W)
• Kilowatt (kW)
• Megawatt (MW)
• Gigawatt (GW)
• Milliwatt (mW)
• Horsepower (mechanical) (hp)
• Horsepower (metric) (PS)
• Horsepower (electric) (hp (E))
• Btu per hour (Btu/h)
• Btu per minute (Btu/min)
• Ton of refrigeration (TR)
• Kilocalorie per hour (IT) (kcal/h)
• Calorie per second (IT) (cal/s)
• Foot-pound force per second (ft·lbf/s)
• Foot-pound force per minute (ft·lbf/min)
• Kilojoule per hour (kJ/h)
• Erg per second (erg/s)