1 J in every unit
Values update with the converter above. Select a row to open that conversion's detailed page.
- Kilojoule0.001 kJ
- Megajoule0.000001 MJ
- Watt-hour0.0002777778 Wh
- Kilowatt-hour0.0000002777778 kWh
- Calorie0.2390057 cal
- Kilocalorie0.0002390057 kcal
- BTU0.0009478171 Btu
- Therm0.000000009478171 th
- Quadrillion BTU9.47817E-19 quad BTU
- Electronvolt6.24151E18 eV
Popular conversions
9 pairsJoule ↔ Kilowatt-hour
J ↔ kWh
Calorie ↔ Joule
cal ↔ J
Kilocalorie ↔ Kilojoule
kcal ↔ kJ
British Thermal Unit ↔ Kilowatt-hour
Btu ↔ kWh
Watt-hour ↔ Kilowatt-hour
Wh ↔ kWh
Joule ↔ Megajoule
J ↔ MJ
Joule ↔ Therm
J ↔ th
Joule ↔ Quad BTU
J ↔ quad BTU
Electronvolt ↔ Joule
eV ↔ J
Unit guides
11 unitsEnergy and Power calculators
2 toolsDetailed guide to Energy and Power
Energy measures an amount of work or heat, distinct from power, which measures the rate energy is transferred (see the separate Power category).
This category brings together practical energy conversions used in electricity billing, heating, food labels, building systems and science. The number can be converted directly; its real-world meaning still depends on the context in which it was measured.
- Physical quantity
- Energy
- SI unit
- Joule
- Common billing unit
- Kilowatt-hour
- Typical use
- Electrical consumption and heat content
Energy, power and billing units
Energy is an amount of work or heat, commonly shown in joules or kilowatt-hours. Power is the rate at which energy is used or produced, commonly shown in watts or kilowatts.
A 2 kW appliance does not use 2 kWh unless it runs for one hour. Check the time period and tariff separately when estimating an energy bill, charging cost or fuel equivalent.
What is energy?
Energy measures an amount of work or heat stored or transferred, not the rate at which it happens.
A kilowatt-hour is an energy unit; the related power unit (kilowatt) has its own conversion category. A 2 kW appliance operating at that power for 3 hours uses 6 kWh of energy.
Joules and metric energy units
The joule (J) is the SI unit of energy. Kilojoules and megajoules use the usual metric prefixes: 1 kJ is 1,000 J and 1 MJ is 1,000,000 J.
Joules are common in physics and engineering because they connect directly to work, heat and electrical energy calculations. They provide a neutral reference when comparing units from different systems.
Watt-hours and electricity bills
A watt-hour is the energy delivered by one watt of power for one hour. It equals 3,600 J, so 1 kWh equals 3.6 MJ. Electricity meters and utility bills normally use kWh because household consumption is much larger than one watt-hour.
Do not read kW and kWh as interchangeable. Kilowatts describe a device's power rating at an instant; kilowatt-hours describe accumulated energy over time. For a cost estimate, multiply power, running time and the applicable electricity tariff.
Calories in food and heat calculations
The small calorie (cal) and kilocalorie (kcal) are energy units. In nutrition, a label's capitalized Calorie commonly means one kilocalorie, not one small calorie. Check the label convention and country before comparing it with a recipe or health record.
Calories and kilocalories also appear in older heat calculations. In international scientific and technical work, joules and kilojoules are generally the clearer reference units.
Btu, therms and electronvolts
Btu (British thermal unit) is widely encountered in heating and cooling equipment, fuel content and building-services specifications. A therm is a much larger fuel-energy unit, often used in gas billing. The exact Btu convention should be stated in formal technical or contractual work.
The electronvolt (eV) is a very small energy unit used in atomic, particle and semiconductor physics. It is not a household energy unit, but makes values at microscopic scales easier to read than a long decimal number of joules.
Energy versus power, capacity and heat rate
Energy is an accumulated quantity. Power is the rate of energy transfer, so 1 W equals 1 J per second. A battery's energy capacity may be given in Wh or kWh, while its charger or inverter is rated in W or kW.
Likewise, Btu is energy whereas Btu per hour is a heat rate (power). Before converting, make sure both sides describe the same physical quantity; this converter converts energy only.
Unit comparison table
| Unit | Symbol | SI equivalent | System | Common use |
|---|---|---|---|---|
| Joule | J | 1 J | SI | Physics, engineering and general energy calculations |
| Kilojoule | kJ | 1,000 J | SI/metric | Food labels, heat and technical reporting |
| Megajoule | MJ | 1,000,000 J | SI/metric | Fuel, heating and larger energy totals |
| Watt-hour | Wh | 3,600 J | Practical electrical unit | Small batteries and device energy capacity |
| Kilowatt-hour | kWh | 3,600,000 J (3.6 MJ) | Practical electrical unit | Electricity meters, bills and battery capacity |
| Calorie | cal | 4.184 J | Non-SI | Older heat calculations |
| Kilocalorie | kcal | 4,184 J | Non-SI | Food energy and nutrition labels |
| British thermal unit | Btu | 1,055.056 J | US customary / non-SI | Heating, cooling and fuel specifications |
| Therm | th | 105.506 MJ | Gas-energy unit | Natural-gas billing and fuel totals |
| Electronvolt | eV | 1.602176634 × 10⁻¹⁹ J | Physics | Atomic, particle and semiconductor physics |
Energy and power units
| Unit | Symbol | Information |
|---|---|---|
| Joule | J | View unit guide |
| Kilowatt-hour | kWh | View unit guide |
| Kilojoule | kJ | View unit guide |
| Calorie | cal | View unit guide |
| Kilocalorie | kcal | View unit guide |
| British Thermal Unit | Btu | View unit guide |
| Watt-hour | Wh | View unit guide |
| Megajoule | MJ | View unit guide |
| Therm | th | View unit guide |
| Quad BTU | quad BTU | View unit guide |
| Electronvolt | eV | View unit guide |