Joule (J)
The SI unit of energy, work and heat: the work done by a force of one newton over one metre, or one watt sustained for one second.
The joule, named after James Prescott Joule, is the coherent SI unit for all forms of energy: mechanical, electrical, thermal and chemical. Energy statistics bodies such as the IEA and the Energy Institute express total energy in joule multiples, notably petajoules (PJ) and exajoules (EJ).
1 kWh = 3.6 x 10⁶ J = 3.6 MJ
1 cal (thermochemical) = 4.184 J; 1 cal (IT) = 4.1868 J
1 BTU (IT) = 1,055.06 J
1 toe = 41.868 GJ; 1 eV = 1.602 x 10⁻¹⁹ J
Prefixes: kJ 10³, MJ 10⁶, GJ 10⁹, TJ 10¹², PJ 10¹⁵, EJ 10¹⁸
Scale references:
- Lifting 1 kg by 1 m on Earth: 9.81 J
- Heating 1 litre of water by 1 K: 4,186 J
- Daily food intake of 2,000 kcal: about 8.4 MJ
- One litre of petrol: about 32 MJ (LHV)
- One kilogram of natural gas: about 50 MJ (LHV)
- Fission of one kilogram of U-235: about 80 TJ
Fuel calorific values are given in MJ/kg or MJ/m³, while electricity is commonly reported in kWh. The fuel energy content calculator converts between them.
Related terms
All terms →- Kilowatt-hour (kWh)
A unit of energy equal to one kilowatt of power sustained for one hour, or 3.6 megajoules; the standard billing unit for electricity.
- Exajoule (EJ)
An SI unit of energy equal to 10¹⁸ joules (277.8 TWh), used to express national and global primary energy supply.
- Watt (W)
The SI unit of power, equal to one joule per second; it measures the rate at which energy is produced, transferred or used.
- BTU (British thermal unit)
A traditional unit of heat, approximately the energy needed to raise one pound of water by one degree Fahrenheit; 1 BTU (IT) = 1,055.06 J.
- Calorific value (HHV / LHV)
The heat released by complete combustion of a unit quantity of fuel; the higher (gross) value includes condensation heat of water vapour, the lower (net) value excludes it.
- Tonne of oil equivalent (toe)
A conventional energy unit equal to 41.868 GJ (10 Gcal, 11.63 MWh), the nominal heat content of one tonne of crude oil, used in energy balances.