The watt-hour (symbol W·h or Wh) is a unit of
energy. It is most commonly used on household
electricity meters in the form of the kilowatt-hour (kW·h or kWh), which is 1,000 watt-hours. It is not used in the International System of Units (
SI), despite being based on the
watt, as the
hour is not an SI unit. The SI unit of energy is the
joule (J), equal to one watt-
second. It is, however, a commonly used unit, especially for measuring
electric energy.1 watt-hour is equivalent to 3,600
joules (1 W x 3600 s), the joule being the canonical SI unit of energy. Thus a kilowatt-hour is 3,600,000 joules or 3.6 megajoules.
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