Grams To Calories Calculator
Convert grams of protein, carbs, fat or alcohol into calories, or work out a mixed food.
100 g of each nutrient
| Nutrient | Factor | Calories | Kilojoules |
|---|---|---|---|
| Protein | 4 kcal/g | 400 kcal | 1,674 kJ |
| Carb | 4 kcal/g | 400 kcal | 1,674 kJ |
| Fat | 9 kcal/g | 900 kcal | 3,766 kJ |
| Alcohol | 7 kcal/g | 700 kcal | 2,929 kJ |
| Fibre | 2 kcal/g | 200 kcal | 837 kJ |
Grams of what?
Mass alone does not determine calories — it depends entirely on the nutrient. The standard figures are the Atwater general factors, in kilocalories per gram:
- Protein — 4
- Carbohydrate — 4
- Fat — 9, more than double the others
- Alcohol — 7
- Fibre — 2, where it is counted at all
kcal = grams × factor
100 g of pure carbohydrate is 400 kcal; 100 g of fat is 900 kcal. Water, vitamins and minerals contribute nothing, which is why a food's total weight tells you very little.
Calories and kilocalories
The "calorie" on a food label is really a kilocalorie —
1,000 thermochemical calories. Europe labels the same quantity in kilojoules,
where 1 kcal = 4.184 kJ. So 400 kcal and 1,674 kJ are the same
energy.
Why label figures do not always add up
Manufacturers may use food-specific Atwater factors rather than the general ones, treat fibre differently, or round each line of the panel independently. A discrepancy of a few percent between the stated calories and the macros multiplied out is normal and not an error.
These are metabolisable energy estimates. How much energy your body actually extracts varies with processing, cooking and the individual.