Gigajoules to Kilowatt-hours (GJ to kWh)

1 gigajoule equals 277.7777778 kilowatt-hours (rounded).

1 gigajoule = 277.7777778 kilowatt-hours

How to convert gigajoules to kilowatt-hours

To convert gigajoules to kilowatt-hours, multiply the number of gigajoules by 277.7777778. The factor is rounded to 10 significant digits. To go the other way, multiply kilowatt-hours by 0.0036.

kilowatt-hours = gigajoules × 277.7777778

Example: 10 gigajoules = 2,777.777778 kilowatt-hours.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Gigajoule (GJ)

Metric (SI)Current unit

One billion joules, roughly the energy in 29 liters of petrol. Used for natural gas and district heating.

One gigajoule is a billion joules, a size that only shows up when something large is being counted. An average lightning bolt carries about that much, and the superconducting magnet of the ATLAS experiment at CERN stores about 1.1 GJ of magnetic energy.

Everyday life can reach it too, just slowly. Filling a car with about 61 liters of gasoline, roughly 16 US gallons, puts in about 2 GJ of combustion energy. A standard refrigerator uses about 4.5 GJ in a year, and an average human heart muscle expends about 3.3 GJ over an 80-year lifetime.

Larger reference points sit nearby. One megawatt-hour is 3.6 GJ, exploding a ton of TNT releases about 4.2 GJ, and a barrel of oil equivalent is about 6.1 GJ. These comparisons explain why gigajoules suit annual household or building energy tallies better than joules or kilojoules.

1 gigajoule = 1,000,000,000 joules (exactly).

Sources: Wikipedia: Orders of magnitude (energy); Wikipedia: Joule

Kilowatt-hour (kWh)

Metric (SI)Current unit

3.6 million joules, the energy used by a 1,000-watt appliance in an hour. The billing unit for household electricity.

Before it was a line on every power bill, the kilowatt-hour had a British nickname: the Board of Trade unit, abbreviated B.T.U. after the government body that regulated the electricity industry until 1942, when the Ministry of Power took over. In India it is still often called simply a unit, and a million of them, written MU, is a gigawatt-hour.

A kilowatt-hour is the energy of a 1 kW device running for an hour, which is 3.6 MJ, or about 3,412 British thermal units. A 100 W television watched for 10 hours uses one, and boiling a liter of water in an electric kettle takes about 0.1. In 2020 the average US household used 893 kWh a month, an average continuous draw of about 1.22 kW.

Utilities multiply the kilowatt-hours consumed by a price per kWh, and larger customers may also pay for peak demand. One common error is writing kW/h, which would mean kilowatts per hour, a rate of change of power, not energy.

1 kilowatt-hour = 3,600,000 joules (exactly).

Sources: Wikipedia: Kilowatt-hour; Wikipedia: British thermal unit; Wikipedia: Watt-hour

Related conversions

See all energy units.