Energy Converter
Convert between Energy units. Choose from 20 different units including Joules, Kilojoules, Megajoules.
Popular Conversions
All Units
| From | Joules (J) |
|---|---|
| Joules (J) | 1 |
| Kilojoules (kJ) | 1000 |
| Megajoules (MJ) | 1000000 |
| Gigajoules (GJ) | 1000000000 |
| Millijoules (mJ) | 0.001 |
| Watt-Hours (Wh) | 3600 |
| Kilowatt-Hours (kWh) | 3600000 |
| Megawatt-Hours (MWh) | 3600000000 |
| Calories (cal) | 4.184 |
| Kilocalories (kcal) | 4184 |
| Calories (nutritional) (Cal) | 4184 |
| BTU (BTU) | 1055.06 |
| Therms (therm) | 105506000 |
| Ergs (erg) | 1e-7 |
| Electron Volts (eV) | 1.602e-19 |
| Kiloelectron Volts (keV) | 1.602e-16 |
| Megaelectron Volts (MeV) | 1.602e-13 |
| Foot-Pounds (ft·lbf) | 1.35582 |
| Horsepower-Hours (hp·h) | 2684520 |
| Tons of TNT (tTNT) | 4184000000 |
The universal currency of physics
Energy is what gets exchanged whenever anything happens: a falling apple, a glowing filament, a digesting meal, a fissioning nucleus. The SI unit is the joule, defined as the work done by one newton acting over one metre. It is a tiny unit by human standards, which is why daily life prefers kilojoules, kilowatt-hours, kilocalories, and BTU, while particle physicists shrink down to electronvolts and astrophysicists cling to the venerable erg.
How so many units survived
Each unit is a fossil of a discipline. The calorie came from 19th-century thermochemistry, defined by warming water. The BTU arose in the British coal and steam industry. The kilowatt-hour was born with electrical billing. The electronvolt emerged from early 20th-century atomic physics, where the energy gained by an electron crossing one volt was a natural ruler. The ton of TNT, equal to exactly 4.184 gigajoules by convention, was adopted to give nuclear yields a familiar yardstick; the Hiroshima bomb is usually quoted at around 15 kilotons, roughly 63 terajoules.
Energy in daily bills and lab notebooks
Electricity meters tick over in kWh. Natural gas in many countries is sold by the therm or megajoule. Nutrition labels list food energy in kcal or kJ depending on the jurisdiction. Heating and cooling specifications, especially in North America, lean on BTU. Particle accelerators publish collision energies in TeV. The erg is essentially extinct outside astrophysics journals, where it persists out of historical inertia.
Traps in the conversion tables
- The food Calorie with a capital C is one kilocalorie, not one calorie. A 200 Calorie snack is 200,000 small calories or about 837 kJ.
- The electronvolt is an energy, not a voltage. A 5 MeV particle has 5 million eV of kinetic energy.
- kWh and kW are not interchangeable. One is energy, the other is power; they differ by a factor of time.
- BTU values vary slightly between definitions (IT, thermochemical, mean); for engineering the IT BTU of 1055.06 J is the usual choice.