Joules to Calories: The Complete Guide
Joules (J) and calories (cal) are both units of energy, but used in very different contexts. Physics and engineering use joules (the SI unit). Nutrition uses calories — but confusingly, what food labels call a "Calorie" (capital C) is actually a kilocalorie (kcal), equal to 1,000 small calories.
The Conversion Formula
calories (cal) = joules ÷ 4.184
kilocalories (kcal) = joules ÷ 4,1841 calorie (thermochemical) = 4.184 joules exactly.
The Calorie Confusion Explained
- 1 cal (small calorie) = 4.184 J — the heat to raise 1 g of water by 1 °C
- 1 kcal (kilocalorie) = 4,184 J — what food labels mean by "Calorie" (capital C)
- 1 food Calorie (Cal) = 1 kcal = 4,184 J
A banana listed as "90 Calories" contains 90 kcal = 376,560 joules of chemical energy. The small calorie (cal) is almost never used in nutrition.
Food Energy Reference (kcal / kJ)
- Apple (medium) = 95 kcal = 397 kJ
- Egg (large) = 78 kcal = 326 kJ
- Slice of bread = 80 kcal = 335 kJ
- 100 g chicken breast = 165 kcal = 690 kJ
- Mars bar (51 g) = 228 kcal = 954 kJ
Why European Food Labels Show kJ
EU regulations require energy to be listed in kilojoules (kJ) first, then kcal in brackets. Both represent the same energy — just different units. To convert kJ to kcal on a label, divide by 4.184.
Convert any energy value instantly: Free joules to calories converter