Kilocalories to kilojoules
Convert kilocalories to kilojoules. Multiply by 4.184, with food label tables and the Calorie / calorie distinction explained.
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The formula
kJ = kcal × 4.184The 4.184 is exact by convention. The thermochemical calorie was defined as 4.184 joules in order to fix a unit that had previously been measured — different definitions of the calorie disagreed in the fourth digit, so the standards bodies picked one and made it a definition.
To go the other way, divide by 4.184. See kJ to kcal.
The label Calorie is this one
A food label’s “Calories” are kilocalories. When a packet says 250 Calories it means 250 kcal, which is 1046 kJ. The lower-case calorie — 4.184 J — appears nowhere in nutrition.
| On a label | Means |
|---|---|
| Calories | kcal |
| kcal | kcal |
| 大卡 | kcal |
| 千卡 | kcal |
| kJ | kJ |
EU and Australian labels must show kilojoules. UK, US, Taiwanese and Hong Kong labels show kilocalories. Many show both, and this conversion is how they agree.
Quick reference
| kcal | kJ |
|---|---|
| 50 kcal | 209 kJ |
| 100 kcal | 418 kJ |
| 200 kcal | 837 kJ |
| 250 kcal | 1046 kJ |
| 500 kcal | 2092 kJ |
| 1000 kcal | 4184 kJ |
| 2000 kcal | 8368 kJ |
| 2500 kcal | 10,460 kJ |
Daily intake
| kcal | kJ | |
|---|---|---|
| Reference intake, women | 2000 | 8368 |
| Reference intake, men | 2500 | 10,460 |
| Sedentary adult | 1800–2200 | 7500–9200 |
| Active adult | 2500–3000 | 10,500–12,600 |
| Endurance athlete, training day | 4000–6000 | 16,700–25,100 |
The “2000 kcal” reference on nutrition labels is a labelling convention, not a recommendation — it exists so that percentage figures have a denominator.
Per gram of nutrient
| Nutrient | kcal/g | kJ/g |
|---|---|---|
| Fat | 9 | 37 |
| Alcohol | 7 | 29 |
| Carbohydrate | 4 | 17 |
| Protein | 4 | 17 |
| Fibre | 2 | 8 |
These are the Atwater factors: averages across food types rather than measurements of any one food. That is why a label’s stated energy and the sum of its macronutrients often differ by a few per cent without either being wrong.
Common foods
| kcal | kJ | |
|---|---|---|
| Apple | 95 | 397 |
| Slice of bread | 80 | 335 |
| Bowl of rice, 200 g | 260 | 1088 |
| Egg | 78 | 326 |
| Chocolate bar, 45 g | 240 | 1004 |
| Can of cola, 330 ml | 139 | 582 |
| Bubble tea, 500 ml | 350 | 1464 |
Estimating in your head
Multiply by 4 and add 5%. 500 kcal × 4 is 2000, plus 100 is 2100 kJ — the true answer is 2092. Multiplying by 4 alone runs 4.4% low, which is close enough to read a label.