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Converters & physics calculator

Power unit converter: watts, horsepower, BTU/h, tons & more

Convert power between watts, kilowatts, megawatts, mechanical, metric and boiler horsepower, BTU per hour, tons of refrigeration, kcal/h and ft·lbf/s. Every unit is shown at once, along with the energy delivered per hour, day and year.

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Results

1 kW = 1.341022 hp · 1 hp = 0.7456999 kW
1 kilowatt (kW) in hp
1.341022hp
Watts
1,000W
Kilowatts
1kW
Horsepower (mech.)
1.341hp
Metric horsepower
1.3596PS
BTU per hour
3,412.1BTU/h
Tons of refrigeration
0.2843TR
Energy in 1 hour
1kWh
Energy per day (24 h)
24kWh
Energy per year (8760 h)
8.76MWh
at constant full power

SI units

Unit1 kW equals1 unit in kW
milliwatt (mW)1,000,0000.000001
watt (W)1,0000.001
kilowatt (kW)11
megawatt (MW)0.0011,000
gigawatt (GW)0.0000011,000,000
terawatt (TW)1 × 10⁻⁹1,000,000,000

Horsepower units

Unit1 kW equals1 unit in kW
horsepower, mechanical (hp, imperial)1.3410220.7456999
horsepower, metric (PS, CV, ch, pk)1.3596220.7354988
horsepower, electrical (746 W)1.3404830.746
boiler horsepower0.1019429.8095

Heating & cooling units

Unit1 kW equals1 unit in kW
BTU per hour (BTU/h)3,412.1420.0002930711
thousand BTU per hour (MBH, kBtu/h)3.4121420.2930711
million BTU per hour (MMBtu/h)0.003412142293.0711
ton of refrigeration (TR, 12,000 BTU/h)0.28434513.516853
kilocalorie per hour (kcal/h)859.84520.001163
megacalorie per hour (Mcal/h)0.85984521.163
calorie per second (cal/s)238.84590.0041868

Mechanical units

Unit1 kW equals1 unit in kW
foot-pound force per second (ft·lbf/s)737.56210.001355818
foot-pound force per minute (ft·lbf/min)44,253.730.00002259697
kilogram-force metre per second (kgf·m/s)101.97160.00980665
erg per second (erg/s)10,000,000,0001 × 10⁻¹⁰

Energy-rate units

Unit1 kW equals1 unit in kW
kWh per day (average power)240.04166667
MWh per year (average power)8.760.1141553
TWh per year (average power)0.00000876114,155
tonne of oil equivalent per year0.75322441.327626
  • Mechanical (imperial) horsepower = 550 ft·lbf/s = 745.700 W; metric horsepower (PS, CV, ch) = 75 kgf·m/s = 735.499 W; electrical horsepower = 746 W exactly; boiler horsepower = 33,475 BTU/h.
  • A ton of refrigeration (12,000 BTU/h) is the heat needed to melt one short ton of ice in 24 hours. Cooling capacity is thermal power: divide by the EER/COP to get electrical input.
  • Energy-rate rows (kWh/day, TWh/yr) express a constant average power; they are handy for comparing demand figures.

How to use the power unit converter

Enter a value, pick the unit you have and the unit you need. The converter shows the answer, then lists all 25 power units at once: SI multiples from milliwatt to terawatt, four kinds of horsepower, the heating and cooling units used by HVAC engineers (BTU/h, MBH, tons of refrigeration, kcal/h), mechanical units (ft·lbf/s, kgf·m/s) and “energy-rate” units such as TWh per year that statisticians use for average demand. It also shows how much energy the power delivers in an hour, a day and a year of continuous operation.

The formula

value_target = value_source × (watts per source unit) ÷ (watts per target unit)

1 hp (mechanical) = 550 ft·lbf/s = 745.700 W 1 PS (metric) = 75 kgf·m/s = 735.499 W 1 BTU/h = 0.293071 W 1 TR = 12,000 BTU/h = 3,516.85 W 1 kcal/h = 1.163 W Energy (kWh) = power (kW) × time (h)

Worked example

The default converts 1 kW to horsepower: 1,000 W ÷ 745.70 W = 1.341 hp, or 1.360 PS. The same kilowatt is 3,412 BTU/h, 860 kcal/h and 0.284 refrigeration tons; running continuously it delivers 24 kWh a day and 8.76 MWh a year.

Quick reference table

From W kW hp BTU/h
1 W 1 0.001 0.001341 3.412
1 kW 1,000 1 1.341 3,412.1
1 MW 10⁶ 1,000 1,341 3.412 million
1 hp (mechanical) 745.7 0.7457 1 2,544.4
1 PS (metric hp) 735.5 0.7355 0.9863 2,509.6
1 boiler hp 9,809.5 9.81 13.15 33,471
1 BTU/h 0.2931 0.000293 0.000393 1
1 ton refrigeration 3,516.9 3.517 4.716 12,000
1 kcal/h 1.163 0.001163 0.00156 3.968
1 ft·lbf/s 1.356 0.001356 0.001818 4.626

Common equipment ratings

Device Typical rating In other units
Split air conditioner 9,000–24,000 BTU/h 2.6–7.0 kW cooling
Gas combi boiler 24–35 kW 82,000–119,000 BTU/h · 20,600–30,100 kcal/h
Family car engine 100 PS 73.5 kW · 98.6 hp
Industrial motor 75 kW 100.6 hp
Onshore wind turbine 4–6 MW 5,400–8,000 hp
Large power station unit 1,000 MW 1.34 million hp

Tips and pitfalls

  1. Thermal vs electrical. BTU/h, tons and kcal/h ratings of air conditioners and heat pumps describe heat moved, not electricity used. Divide by the COP or EER to get electrical input.
  2. European car brochures use PS (or CV, ch). The same engine shows about 1.4% more “horsepower” in PS than in US hp.
  3. MBH means thousand BTU/h, not million. HVAC catalogues get this wrong surprisingly often. Million BTU per hour is written MMBtu/h.
  4. Apparent vs real power. Generators and transformers are rated in kVA; convert to kW with the power factor using the kVA to kW calculator.
  5. Average power. A country consuming 50 TWh a year has an average demand of 5.7 GW, a useful figure to set against plant capacities.

Limitations

All factors are exact definitions or internationally agreed constants. Ratings on nameplates are measured under specific conditions (temperature, voltage, altitude), so actual output of engines, motors and heat pumps can differ from the converted figure.

Method & assumptions

All units are converted via watts: valueto = valuefrom × Wfrom ÷ Wto. Energy over time = power × hours (1 kW for 1 h = 1 kWh).

Frequently asked questions

How many horsepower is 1 kW?
1 kW = 1.341 mechanical (imperial) horsepower = 1.360 metric horsepower (PS). Conversely, 1 hp = 0.7457 kW and 1 PS = 0.7355 kW.
What is the difference between hp, PS and bhp?
Mechanical horsepower (hp) is 550 foot-pounds per second, 745.7 W, used in the US and UK. Metric horsepower (PS, CV, ch, pk) is 75 kilogram-force metres per second, 735.5 W, used for cars in continental Europe. 'Brake horsepower' (bhp) is a measurement condition (power at the crankshaft), usually in mechanical hp, whereas 'boiler horsepower' is a completely different steam-boiler unit of 9.81 kW.
How many kW is 12,000 BTU/h?
12,000 BTU/h = 3.517 kW of thermal power, also called one ton of refrigeration. A '12,000 BTU' air conditioner provides about 3.5 kW of cooling and draws roughly 1–1.2 kW of electricity at an EER of 3.
How many kW is a ton of refrigeration?
One refrigeration ton (TR) = 12,000 BTU/h = 3.517 kW. It derives from the heat needed to melt one short ton (907 kg) of ice in 24 hours.
How do I convert kcal/h to kW?
Multiply by 0.001163. A boiler rated at 24,000 kcal/h delivers 27.9 kW; 1 kW = 860 kcal/h.
What is the difference between kW and kWh?
kW measures power, the rate of energy use at a given moment. kWh measures energy: power multiplied by time. A 2 kW heater running for 3 hours uses 6 kWh. For energy units use the energy unit converter.

Sources & references

  1. NIST Special Publication 811 — Guide for the Use of the SI, Appendix B (conversion factors)
  2. BIPM — The International System of Units (SI Brochure, 9th edition)
  3. ASHRAE Handbook — Fundamentals: units and conversions (refrigeration ton, BTU/h)

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