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kJ to kcal — the converter for UK labels
A UK label carries both units: kilojoules first, then kilocalories. Type a figure into either box and the other follows, on the fixed basis 1 kcal = 4.184 kJ. Free, no sign-up, and the sum runs in your browser.
On a label both figures appear, in the order kJ / kcal.
The formula, both ways
- kJ to kcal: divide by 4.184. 1,000 kJ ÷ 4.184 = 239 kcal.
- kcal to kJ: multiply by 4.184. 239 kcal × 4.184 = 1,000 kJ.
kJ to kcal — the table
| Kilojoules | Kilocalories |
|---|---|
| 100 kJ | 23.9 kcal |
| 200 kJ | 47.8 kcal |
| 500 kJ | 119.5 kcal |
| 1,000 kJ | 239.0 kcal |
| 2,000 kJ | 478.0 kcal |
| 8,400 kJ | 2,007.6 kcal |
kcal to kJ — the table
| Kilocalories | Kilojoules |
|---|---|
| 50 kcal | 209 kJ |
| 100 kcal | 418 kJ |
| 200 kcal | 837 kJ |
| 500 kcal | 2,092 kJ |
| 2,000 kcal | 8,368 kJ |
Why a UK label shows both
Because the law names both. Annex XV of the retained Regulation (EU) No 1169/2011 sets the units of the nutrition declaration as “energy (kilojoules (kJ) and kilocalories (kcal))” and gives the order of presentation as “energy kJ/kcal”. Kilojoules come first; the kilocalorie figure is not an optional extra.
How the energy value is calculated
Not by converting one number into the other, but from the nutrients. Annex XIV gives the factors, and both columns come from the same table — which is why the two figures on a label are consistent with each other and with the rest of the declaration.
| Per gram of | kJ | kcal |
|---|---|---|
| carbohydrate (except polyols) | 17 | 4 |
| protein | 17 | 4 |
| fat | 37 | 9 |
| fibre | 8 | 2 |
| polyols | 10 | 2.4 |
| alcohol (ethanol) | 29 | 7 |
| organic acid | 13 | 3 |
| salatrims | 25 | 6 |
| erythritol | 0 | 0 |
📘 Wording and figures quoted from the primary source on 21 October 2026: the retained Regulation (EU) No 1169/2011, Annexes XIV and XV, on legislation.gov.uk.
Where a US label differs
A US Nutrition Facts panel must show Calories — the capital-C Calorie is the kilocalorie — and may add kilojoules in parentheses. It is also worked out with different factors: 21 CFR 101.9(c)(1)(i) allows the general factors of 4, 4 and 9 calories per gram for protein, carbohydrate and fat, so fibre is not treated the way the UK factor of 2 kcal per gram treats it. The US converter goes through that side.
Frequently asked questions
How many kcal is 1,000 kJ?
239 kcal. 1,000 ÷ 4.184 = 239.0.
Does a UK label have to show both kJ and kcal?
Yes. Annex XV sets the units as “energy (kilojoules (kJ) and kilocalories (kcal))” and the order as “energy kJ/kcal”.
How is the energy value worked out in the first place?
From the nutrients, with the Annex XIV factors in the table above — not by converting one figure into the other.
Why does a US label look different?
Different rules and different factors — see the section above.
From the number to a finished label
Converting one figure is a start; a label needs the whole declaration. Foodlex works it out from your recipe on the UK composition tables — see what it does, or start in the app.