Kilocalorie (kcal) to Kilojoule (kJ)
Convert kilocalories to kilojoules. UK food labels list energy as kilojoules (kJ) first, with kilocalories (kcal) in brackets — for example "837 kJ (200 kcal)". One kilocalorie is exactly 4.184 kilojoules.
Frequently asked questions
1 kilocalorie (kcal) equals 4.184 kilojoules (kJ). This is an exact definition: 1 cal = 4.184 J, so 1 kcal = 4.184 kJ.
The UK Reference Intake (RI) is 8,400 kJ (2,000 kcal) per day for an average adult. This is the figure shown on the front of most UK food packaging as a percentage of the daily reference value.
Multiply the number of kilocalories by 4.184. Example: 500 kcal × 4.184 = 2,092 kJ. For a quick mental estimate, multiply by 4 then add roughly 18%.
EU Regulation 1169/2011 — retained in UK law after Brexit — requires energy to be declared in kilojoules, with kilocalories shown alongside. Kilojoules are the SI unit for energy; kilocalories are the traditional unit most consumers recognise for food.