kcal to kJ Converter

About the kcal to kJ Converter

Convert food energy between kilocalories and kilojoules — type in either box and the other updates. One kilocalorie is exactly 4.184 kJ (the thermochemical calorie is 4.184 J), so kJ = kcal × 4.184 and kcal = kJ ÷ 4.184: 100 kcal is 418.4 kJ and 1,000 kJ is about 239 kcal. The “Calories” (Cal) on a food label are kilocalories, so 250 Calories is 1,046 kJ.

Under the converter, Per 100 g, per serving and per pack takes the energy from a label’s per-100 g column and works out a serving and the whole pack in both units, with the share of the 2,000 kcal adult reference intake. Check a label’s energy from its nutrients recalculates it from the grams of fat, carbohydrate, protein, fibre and alcohol with the official EU and Indian (FSSAI) factors — which is why a label’s kJ and kcal are not always exactly 4.184 apart.

Common uses

• Reading a food label from Australia, New Zealand or the EU in kcal, or an Indian or US label in kJ.
• Working out the energy of one serving or a whole pack from the per-100 g column.
• Diet and fitness apps that count kJ when you think in Calories, or the other way round.
• Checking a recipe’s or a label’s energy from its fat, carbohydrate and protein.

Calories, calories and kilocalories

The kilocalorie (kcal) is 1,000 calories, and the thermochemical calorie used for food is exactly 4.184 J, so 1 kcal = 4.184 kJ (NIST SP 811, Appendix B.8). NIST calls the “large calorie” or “kilogram calorie” an obsolete name for the kilocalorie, the calorie of food energy, and notes that the “kilo” is usually dropped in practice — which is why labels that print Calories, as on US Nutrition Facts panels, mean kilocalories. A small calorie (cal) is a thousandth of that, 4.184 J.

Steam tables and heating engineering use the International Table calorie, 4.1868 J, which is 0.07 % larger. This page uses the thermochemical 4.184 J, the value usually used for food energy.

kJ first or kcal only: what each label shows

• European Union: Regulation (EU) No 1169/2011 requires the energy per 100 g or 100 ml in both units, in the order “kJ/kcal” (Annex XV), optionally also per portion; the adult reference intake is 8,400 kJ/2,000 kcal (Annex XIII, Part B).
• Australia and New Zealand: Food Standards Code, Standard 1.2.8 gives the average energy per serving and per 100 g “in kilojoules or both in kilojoules and in kilocalories” — so a label may show kJ alone.
• India: the FSSAI (Labelling and Display) Regulations, 2020 (regulation 5(3)) ask for the energy value in kcal per 100 g, 100 ml or single pack, with the per-serve share of a 2,000 kcal day.

The joule, and so the kilojoule, is the SI unit of energy; the kilocalorie is not an SI unit, but it remains in use for food.

Why kJ ÷ 4.184 does not always match the label

Labels do not convert one figure into the other: they calculate both from the grams of each nutrient, with fixed factors per gram. In the EU (Annex XIV) fat counts 37 kJ or 9 kcal per gram, carbohydrate and protein 17 kJ or 4 kcal, fibre 8 kJ or 2 kcal, alcohol 29 kJ or 7 kcal and polyols 10 kJ or 2.4 kcal. Those pairs were rounded separately — 37 ÷ 9 is 4.11 and 17 ÷ 4 is 4.25 — so a fatty food’s kJ is a little less than 4.184 × its kcal and a starchy one’s a little more. FSSAI uses the same kcal factors, except 2 kcal per gram for polyols, and gives none for salatrims. Rounding each figure to a whole number adds a little more.

Limitations

• This converts energy units and scales label values. It does not estimate the energy of a food without a label, or the energy you burn: see the Calories Burned Calculator.
• 2,000 kcal is the reference value labels use, not anyone’s own need; the TDEE Calculator estimates that.
• The label calculator rounds like a label: whole kcal and kJ from 10 up, one decimal below.
• The nutrient check covers the main nutrients and organic acids; erythritol counts 0, and salatrims are in the factor table only.

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