Power Converter

Power is the rate at which energy is used or produced. The watt is the SI unit, while horsepower is common for engines and BTU per hour for heating and cooling equipment.

This converter helps compare the output of motors, appliances and HVAC systems quoted in different units.

Horsepower is not a single unit. Mechanical horsepower, used in the US and UK, is 745.6999 watts. Metric horsepower (the PS or CV figure quoted across most of Europe and Asia) is 735.49875 watts. They differ by 1.39%, which is enough to change a headline number.

A car advertised at 200 PS is producing about 197.3 mechanical horsepower, not 200. In the other direction, 100 kW is 134.1 mechanical horsepower or 136.0 metric: the same engine, two different figures, neither of them wrong.

• This converter lists both separately. Which one a specification uses is usually determined by the market it was written for.
• Electrical horsepower, used for motor ratings, is defined differently again at exactly 746 W.
• When comparing vehicles across markets, convert both to kilowatts first, as it is the unambiguous unit.

A power rating describes output under specific conditions, and real devices rarely sit at it. A motor rated at 2 kW draws that at full load and considerably less when lightly loaded; an appliance rated at 1.5 kW may cycle on and off rather than drawing continuously.

Efficiency drives a further wedge between input and output. A motor rated at 2 kW of mechanical output draws more than 2 kW of electrical input, with the difference lost as heat, so the rating on the nameplate and the figure on the meter are not the same measurement.

• Heating and cooling equipment is rated in BTU per hour, which is a power unit despite the "hour" in its name, about 0.293 W per BTU/h.
• Peak and continuous ratings differ substantially on motors, generators and power supplies.
• To estimate running cost, multiply average power by hours of use to get kWh, then apply the tariff. The rating alone will overstate it.