Joules to Calories Converter

Energy is the capacity to do work, and its SI unit is the joule (J) — the work done when a force of one newton moves something one metre. A joule is small, so different fields adopted their own units. Nutrition uses calories: the food “Calorie” with a capital C is actually a kilocalorie (kcal), equal to 4,184 joules, while food labels in many countries also show kilojoules. Electricity is billed in kilowatt-hours — one kWh is 3.6 million joules, the energy of a 1,000-watt appliance running for an hour. Heating and gas use the British thermal unit (BTU) and the therm (100,000 BTU), fuels are measured in barrels or tonnes of oil equivalent, mechanics uses foot-pounds, physics uses the electronvolt (the energy an electron gains across one volt, about 1.6 × 10⁻¹⁹ J), and explosive yield is quoted in tons of TNT (one ton = 4.184 gigajoules). One subtlety: the calorie has two slightly different definitions — the thermochemical calorie (4.184 J, used here) and the International Table calorie (4.1868 J) — and this tool includes both so you can match whichever a source uses. Every unit is stored as its exact number of joules, so any conversion is just the input turned into joules and then into the target unit.