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Convert between joules, calories, kWh, and BTU.
⚡ Food "Calories" are actually kilocalories (kcal). 1 kcal = 4.184 kJ.
This tool converts between energy units: joules, calories, kilowatt-hours, BTU, and electron-volts. Energy appears in nutrition, electricity, physics, and heating.
Food labels use Calories with a capital C, which actually means kilocalories (kcal). One food Calorie = 1,000 small calories = 4,184 joules. So a "200 Calorie" snack contains 200,000 small calories — but everyone means kcal when discussing food.
The Energy Converter converts energy converterfrom one unit to another using the exact internationally defined conversion factors. Type a value, choose your source and target units, and the converted result is shown instantly — no waiting, no page reload.
Manual conversion is error-prone because it means memorizing ratios (how many feet in a meter, how many pints in a liter). This tool removes that friction: the conversion factor is built in, and the math is done to full precision with no rounding until the final displayed number.
Common uses: people reach for this tool when they need to look up a joules to calories converter, kwh to joules calculator, btu to joules online, or calorie to kilojoule converter.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The Energy Converter is based on the following formula:
1 cal = 4.184 J 1 kcal = 1 food Calorie = 4184 J 1 kWh = 3,600,000 J = 3.6 MJ 1 BTU = 1055.06 J 1 eV = 1.602176634 × 10⁻¹⁹ J
Variables: J = joule, the SI unit (1 watt acting for 1 second) cal = small calorie kcal = kilocalorie, the food Calorie with capital C kWh = kilowatt-hour BTU = British thermal unit eV = electronvolt
The joule is one watt-second. The calorie was defined as the energy to warm 1 g of water by 1 °C and is now fixed at exactly 4.184 J; food Calories are kilocalories, 1000 times larger. A kWh is what a 1000 W appliance uses in one hour, exactly 3.6 MJ.
Worked example: A 2000 kcal daily diet in SI units: J = 2000 × 4184 = 8,368,000 J = 8.37 MJ A 2 kW heater running for 3 h: 2 × 3 = 6 kWh = 6 × 3.6 = 21.6 MJ
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