Here is the open secret of American food labels: the "Calories" they list are actually kilocalories. One kilocalorie (kcal) is 1,000 small calories and equals 4,184 joules — the energy needed to heat a kilogram of water by one degree Celsius. A 250-Calorie candy bar is 250 kcal, which is 1,046,000 joules. European labels skip the confusion and print kilojoules instead: that same bar shows 1,046 kJ. The kilocalorie is the hinge between the nutrition world and the physics world, and this page translates it into every unit each side uses.

Type your value in the Kilocalories (kcal) box and watch four translations appear: Calories (cal) at 1,000 each, Joules (J) at 4,184 each, Kilojoules (kJ) at 4.184 each, and Kilowatt-hours (kWh) at 0.00116222 each. The 100 kcal example — about one banana — is 100,000 cal, 418,400 J, 418.4 kJ, and 0.116 kWh. That last figure is oddly practical: 100 kcal of food energy could run a 100-watt bulb for just over an hour. Runners converting treadmill readouts, dieters decoding European packaging, and students doing calorimetry homework all need the same factors. Remember the pair that unlocks everything: 1 kcal = 1,000 cal = 4,184 J.

With the pre-filled defaults — Kilocalories (kcal) 100 — the Kilocalorie Converter returns Calories (cal) 100,000.0, Joules (J) 418,400.00, Kilojoules (kJ) 418.4000, Kilowatt-hours (kWh) 0.116222. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.