Energy Units

Electricity - like most other commodities - is sold by the unit.

But what precisely is a kilowatt? And what’s the difference between a kilowatt, a megawatt and a gigawatt?

Kilowatt: The kilowatt (kW) is the standard metric measure of electrical power and is equivalent to 1,000 watts. The kilowatt hour (kWh) - the actual rate of energy consumption - gives us the ‘unit’. A heater rated at 1000 watts (W), for example, running for an hour would use one kWh.  The Imperial measurement of energy, first devised by James Watt inventor of the steam engine, is horsepower. He calculated that a horse could lift 330 pounds, 100 feet in a minute. A kilowatt is the equivalent of 1.3 horsepower, roughly one hundredth the power output of an average family saloon car.

Megawatt: A megawatt (MW) is a million watts, or the equivalent of 1,000 kilowatts. A megawatt could power over a thousand homes.

Gigawatt: A gigawatt (GW) is one thousand million watts, or 1,000 megawatts, of electricity. One gigawatt translates to approximately enough electricity to meet the needs of 604,833 households, 1,451,600 people or around 1per cent of the UK energy supply.

The tables below show the conversion factors for converting between different units of energy and typical calorific values of fuels.

Note: the calorific values were updated September 2008.

The following table gives the number you need to multiply by to get from a variety of different units to kWh.