Energy unit converter

The calculator converts energy between joules, kilojoules, watt-hours, kilowatt-hours and megawatt-hours. Choose the unit of the energy you enter and the unit of the result next to the boxes. Electricity meters count in kilowatt-hours, and one kWh is 3,600 kJ, or 3.6 million joules.

How it works

The joule is the basic unit of energy. A watt-hour is the energy used by an appliance with a power of 1 W for one hour. An hour has 3,600 seconds and 1 W is 1 joule per second, so 1 Wh = 3,600 J.

A few typical conversions:

• 1 kWh = 3,600 kJ = 3,600,000 J,
• 1,000 kJ ≈ 0.28 kWh,
• 2.8 MWh of electricity a year for a flat = 2,800 kWh,
• a 50 Wh laptop battery = 180 kJ.

Things to watch out for

Joules and watt-hours are not converted by a factor of a thousand but by 3,600, because the seconds in an hour come into play. Anyone who divides joules by a thousand and calls the result kWh is out by a factor of 3,600.

Watch the difference between energy and power: kWh is energy, kW is power. Power units are converted with the power unit converter, and consumption from a known power and time with the appliance energy use calculator.

Food packaging shows kilojoules and kilocalories: 1 kcal is about 4.184 kJ. The calculator does not offer calories.