Energy Converter
Convert any energy unit to another with this free energy converter. It supports 9 units including joules, kilojoules, calories, kilocalories, watt hours, kilowatt hours, and more. Pick a conversion below for a dedicated calculator, formula, and reference table. For example, 1 J = 0.001 kJ.
All energy conversions
Joule → KilojouleJoule → CalorieJoule → KilocalorieJoule → Watt HourJoule → Kilowatt HourJoule → ElectronvoltJoule → British Thermal UnitJoule → Foot-PoundKilojoule → JouleKilojoule → CalorieKilojoule → KilocalorieKilojoule → Watt HourKilojoule → Kilowatt HourKilojoule → ElectronvoltKilojoule → British Thermal UnitKilojoule → Foot-PoundCalorie → JouleCalorie → KilojouleCalorie → KilocalorieCalorie → Watt HourCalorie → Kilowatt HourCalorie → ElectronvoltCalorie → British Thermal UnitCalorie → Foot-PoundKilocalorie → JouleKilocalorie → KilojouleKilocalorie → CalorieKilocalorie → Watt HourKilocalorie → Kilowatt HourKilocalorie → ElectronvoltKilocalorie → British Thermal UnitKilocalorie → Foot-PoundWatt Hour → JouleWatt Hour → KilojouleWatt Hour → CalorieWatt Hour → KilocalorieWatt Hour → Kilowatt HourWatt Hour → ElectronvoltWatt Hour → British Thermal UnitWatt Hour → Foot-PoundKilowatt Hour → JouleKilowatt Hour → KilojouleKilowatt Hour → CalorieKilowatt Hour → KilocalorieKilowatt Hour → Watt HourKilowatt Hour → ElectronvoltKilowatt Hour → British Thermal UnitKilowatt Hour → Foot-PoundElectronvolt → JouleElectronvolt → KilojouleElectronvolt → CalorieElectronvolt → KilocalorieElectronvolt → Watt HourElectronvolt → Kilowatt HourElectronvolt → British Thermal UnitElectronvolt → Foot-PoundBritish Thermal Unit → JouleBritish Thermal Unit → KilojouleBritish Thermal Unit → CalorieBritish Thermal Unit → KilocalorieBritish Thermal Unit → Watt HourBritish Thermal Unit → Kilowatt HourBritish Thermal Unit → ElectronvoltBritish Thermal Unit → Foot-PoundFoot-Pound → JouleFoot-Pound → KilojouleFoot-Pound → CalorieFoot-Pound → KilocalorieFoot-Pound → Watt HourFoot-Pound → Kilowatt HourFoot-Pound → ElectronvoltFoot-Pound → British Thermal Unit
About these units
Joule (J)
- Definition
- The joule (J) is the SI unit of energy, the work done by a force of one newton over one meter.
- History
- Named after physicist James Prescott Joule, who studied the link between heat and work.
- Current use
- Joules measure energy, work, and heat throughout science and engineering.
Kilojoule (kJ)
- Definition
- A kilojoule (kJ) is 1,000 joules, a practical size for food energy and mechanical work.
- History
- It is a metric multiple of the joule.
- Current use
- Kilojoules express food energy on nutrition labels in many countries.
Calorie (cal)
- Definition
- A calorie (cal) is the energy needed to raise one gram of water by one degree Celsius, about 4.184 joules.
- History
- Defined in the 19th century, the small calorie was later joined by the larger food Calorie.
- Current use
- Calories appear in chemistry and, as kilocalories, in nutrition.
Kilocalorie (kcal)
- Definition
- A kilocalorie (kcal) is 1,000 small calories — the "Calorie" used on food labels.
- History
- It was adopted by nutritionists as a practical measure of food energy.
- Current use
- Kilocalories (food Calories) measure the energy content of food and diets.
Watt Hour (Wh)
- Definition
- A watt-hour (Wh) is the energy of one watt sustained for one hour, equal to 3,600 joules.
- History
- It arose with the electricity industry as a practical billing unit.
- Current use
- Watt-hours rate batteries and small energy stores.
Kilowatt Hour (kWh)
- Definition
- A kilowatt-hour (kWh) is 1,000 watt-hours, the standard unit on electricity bills.
- History
- It became the billing unit as household electricity spread.
- Current use
- Kilowatt-hours measure home electricity use and EV battery capacity.
Electronvolt (eV)
- Definition
- An electronvolt (eV) is the energy gained by an electron moving through a one-volt potential, a tiny amount of energy.
- History
- It became standard in atomic and particle physics in the 20th century.
- Current use
- Electronvolts measure energies of particles, photons, and chemical bonds.
British Thermal Unit (BTU)
- Definition
- A British thermal unit (BTU) is the energy needed to raise one pound of water by one degree Fahrenheit.
- History
- It developed with steam engineering in Britain and the United States.
- Current use
- BTUs rate heating, air-conditioning, and appliance energy in the US.
Foot-Pound (ft·lb)
- Definition
- A foot-pound (ft·lb) is the work done by a one-pound force acting over one foot, about 1.356 joules.
- History
- It comes from the imperial system of mechanics.
- Current use
- Foot-pounds express torque and energy in US engineering and firearms.
Frequently asked questions
What energy units can I convert?
This energy converter supports 9 units: joules, kilojoules, calories, kilocalories, watt hours, kilowatt hours, electronvolts, british thermal units, foot-pounds. Select any pair below to open a dedicated converter with a formula and conversion table.
How accurate is the energy converter?
Conversions use exact definitional factors, so results are accurate to the precision you need for science, engineering, and everyday use. Values are rounded only for display.
Is the energy converter free?
Yes. Every energy conversion is completely free, needs no sign-up, and runs entirely in your browser — your inputs never leave your device.
Free, private, and instant — every conversion runs in your browser.
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