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ToolBoxGenie

Power Converter

Converters · Added 15 August 2026

Convert power between watts, horsepower, BTU per hour and tons of refrigeration. Horsepower is three different units depending on who is quoting it — mechanical, metric and electrical — and all three are listed separately here, because using the wrong one puts a car's figure out by about 1.4%.

Result

1 hp in kilowatt

0.745699872 kW

1 hp = 0.745699872 kW

The same value in every unit

Watt (W)
745.699872
Milliwatt (mW)
745,699.872
Kilowatt (kW)
0.745699872
Megawatt (MW)
0.000745699872
Gigawatt (GW)
7.4570e-7
Horsepower (mechanical) (hp)
1
Horsepower (metric, PS) (PS)
1.01386967
Horsepower (electrical) (hp(E))
0.999597683
BTU per hour (BTU/h)
2,544.43358
Ton of refrigeration (TR)
0.212036131
Kilocalorie per hour (kcal/h)
641.615568
Foot-pound per second (ft·lbf/s)
550

Metric horsepower (PS, used by most European carmakers) is about 1.4% smaller than mechanical horsepower, so a 200 PS engine is roughly 197 hp. Quoting one figure with the other label is the most common power-conversion error there is.

How to use the power converter

  1. 1Enter the power figure you have.
  2. 2Pick its unit. For a car, check whether the figure is hp (mechanical) or PS (metric).
  3. 3Choose the unit you want; the result appears immediately.
  4. 4The table shows the same power in every unit, including air-conditioning units.
  5. 5Swap to reverse the conversion.

Examples

Car engine output

Input
150 kW
Result
201.15 hp · 203.94 PS

European manufacturers usually quote PS; the same engine is a slightly smaller number in mechanical horsepower.

Air conditioner capacity

Input
12,000 BTU/h
Result
1 ton of refrigeration · 3.52 kW

A 'one-ton' air conditioner is defined as 12,000 BTU per hour — the rate that would melt a ton of ice in a day.

A kettle

Input
3 kW
Result
4.02 hp · 10,235 BTU/h

A domestic kettle draws about the same power as a small motorcycle engine produces.

About the power converter

Where horsepower came from

James Watt needed a way to sell steam engines to people who were currently using horses, and a comparison with the animal they would be replacing was the obvious sales pitch. He measured the rate at which a mill horse could raise weight and rounded it to 33,000 foot-pounds per minute, which became one horsepower. It was a marketing unit that turned out to be durable.

The metric world later defined its own version in metric units — 75 kilogram-force metres per second — and got a slightly different number. Because neither definition displaced the other, the same engine can be honestly described with two different figures, and both appear in manufacturer literature depending on the market.

Real horses, incidentally, comfortably exceed one horsepower in short bursts; a fit horse can sustain something closer to 15 horsepower briefly. Watt's figure describes sustained work over a full shift, which is the useful comparison for a machine expected to run all day.

The watt, and why it is the sensible unit

The watt is defined without reference to any animal or engine: one joule per second. That definition connects it directly to every other mechanical and electrical quantity, which is why it dominates engineering. Electrical power is voltage times current; mechanical power is force times velocity, or torque times angular velocity. All of these come out in watts without a conversion factor.

That connectedness is the practical argument for using watts. Working in horsepower means carrying a conversion factor into every calculation that touches electricity, heat or torque. Working in watts means the units cancel on their own, which removes an entire category of error.

It also makes cross-domain comparisons legible. A 2 kW kettle, a 2 kW electric motor and a 2 kW heater are all consuming energy at the same rate, and saying so in horsepower would obscure rather than clarify the point. The horsepower figures survive in cars and boats mostly because buyers are used to them.

Frequently asked questions

What is the difference between hp and PS?
They are different definitions of horsepower. Mechanical horsepower is 550 foot-pounds per second, about 745.7 watts, and is standard in the UK and US. Metric horsepower — written PS in Germany, CV in France, pk in the Netherlands — is 75 kilogram-force metres per second, about 735.5 watts. Metric horsepower is roughly 1.4% smaller, so a car rated at 200 PS is about 197 hp. Both are quoted on car specifications and they are frequently mixed up.
Why is air conditioning measured in tons?
It dates from before mechanical refrigeration, when buildings were cooled with harvested ice. One ton of refrigeration is the rate of cooling that would melt one short ton of ice over 24 hours, which works out at 12,000 BTU per hour or about 3.517 kW. The unit stuck even though nobody delivers ice any more, which is why an air conditioner's capacity is quoted in a unit of weight.
How is power different from energy?
Power is a rate, energy is a total. A 2 kW heater has a power of 2 kilowatts whether it runs for a minute or a day; the energy it uses depends on how long it runs. Your electricity meter records energy in kilowatt-hours, which is power multiplied by time. For converting joules, kWh, calories or BTU, use the energy converter.
Is a kilowatt of electricity the same as a kilowatt of engine output?
As a unit, yes — a watt is a watt. But the figures are usually measured at different points. An engine's power rating is what it produces at the crankshaft, before losses through the gearbox and drivetrain, so the power actually reaching the wheels is lower. An appliance's rating is what it draws from the supply, which is more than the useful output for anything less than 100% efficient. Comparing the two directly compares an output with an input.

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