- Enter Energy — Type any numeric value.
- Select Units — Choose from 12 energy units: J, kJ, MJ, cal, kcal, Wh, kWh, eV, BTU, ft·lbf, erg, therm.
- See Results — Real-time conversion with all equivalents.
- Copy — Click 'Copy' to copy result.
Energy Converter — Convert Between Energy Units
The Energy Converter is a free, instant-use tool for converting between 12 energy and work units. Whether you're calculating electricity costs, analyzing food nutrition, working on physics problems, or comparing fuel sources, this tool provides accurate real-time conversions across scientific, industrial, and everyday units.
All calculations run entirely in your browser. No data is sent to any server.
Supported Units
- Joule (J) — The SI unit of energy. One joule equals one newton-meter or one watt-second. Named after James Prescott Joule. The fundamental unit for all energy calculations.
- Kilojoule (kJ) — 1,000 joules. Used in nutrition labeling in most countries outside the US (e.g., "1,000 kJ per serving").
- Megajoule (MJ) — 1,000,000 joules. Used for larger energy quantities like fuel energy content and industrial processes.
- Calorie (cal) — The thermochemical calorie: 4.184 J. The energy needed to raise 1 gram of water by 1°C.
- Kilocalorie (kcal) — 1,000 calories = 4,184 J. The food Calorie (capital C) used on nutrition labels in the US. When someone says "a 2,000 calorie diet," they mean 2,000 kcal.
- Watt-hour (Wh) — 3,600 J. Energy consumed by a 1-watt device over one hour. Used for battery capacity specifications.
- Kilowatt-hour (kWh) — 3,600,000 J. The standard unit for electricity billing. A typical US household uses about 900 kWh per month.
- Electronvolt (eV) — 1.602 × 10⁻¹⁹ J. Used in particle physics, quantum mechanics, and semiconductor physics. X-ray energies are measured in keV; particle accelerators in GeV or TeV.
- BTU — 1,055 J. British Thermal Unit. Used in HVAC, heating, and energy industries in the US. The energy to raise 1 pound of water by 1°F.
- Foot-pound force (ft·lbf) — 1.356 J. Used in US engineering for mechanical work and torque.
- Erg — 10⁻⁷ J. CGS unit of energy. Used in some astrophysics contexts.
- Therm — 100,000 BTU = 105.5 MJ. Used for natural gas billing in the US and UK.
Key Conversion Factors
- 1 kWh = 3,600,000 J = 3.6 MJ = 3,412 BTU = 860 kcal
- 1 kcal = 4,184 J = 3.968 BTU = 1.163 Wh
- 1 BTU = 1,055 J = 0.252 kcal = 0.000293 kWh
- 1 therm = 100,000 BTU = 29.3 kWh = 105.5 MJ
Features
- 12 Units — Covers SI, CGS, imperial, electrical, thermal, and atomic scales.
- Real-Time — Instant conversion as you type.
- All-Unit View — See all 11 equivalents simultaneously.
- Swap & Copy — Quick direction swap and clipboard copy.
Common Use Cases
- Electricity — Convert kWh to MJ for energy analysis and cost calculation.
- Nutrition — Convert between kcal and kJ for food labeling.
- Physics — Convert between joules, eV, and ergs for calculations.
- HVAC — Convert between BTU and kW for heating/cooling sizing.
- Gas Billing — Convert therms to kWh for energy comparison.
Privacy
All conversions run in your browser. No data is transmitted. Works offline.