The 4/4/9 formula
Protein and carbohydrate are commonly estimated at 4 calories per gram. Fat is estimated at 9 calories per gram. Multiply each macro, then add the results.
30g protein + 50g carbs + 20g fat = 120 + 200 + 180 = 500 estimated calories.
How the macro percentages work
The calculator divides the calories from each macro by the 4/4/9 total. It shows the share of estimated calories, not the share of food weight. If every input is zero, all three percentages stay at zero.
Starting with a calorie target and percentages instead? Use the macro split calculator for the reverse conversion or read the worked percentages-to-grams guide.
Why the result may not match a label
Food labels use permitted rounding rules. Total carbohydrate includes dietary fiber, and food-specific energy factors can differ from the general formula. A large gap can also point to the wrong serving, unit, or database record.
Read why macros do not always add up to label calories before changing a packaged-food entry.
How many calories in 100g of one macro?
A common question, and the answer follows straight from the factors:
| Nutrient | Per gram | 100 grams |
|---|---|---|
| Protein | 4 kcal | 400 Calories |
| Carbohydrate | 4 kcal | 400 Calories |
| Fat | 9 kcal | 900 Calories |
| Alcohol | 7 kcal | 700 Calories |
One caution worth attaching to that table: 100g of protein is not 100g of a protein food. A chicken breast is roughly 31g of protein per 100g of meat, so 100g of protein is closer to 320g of chicken. The calories in 100 grams guide shows that difference across thirteen foods.
Alcohol is the fourth energy nutrient
It is missing from most macro calculators, including the inputs above, because it is not a macro in the usual sense. It still carries 7 kcal per gram, between carbohydrate and fat.
That is why 4/4/9 arithmetic falls apart on drinks. A spirit with no carbohydrate, protein or fat still has calories, and a 4/4/9 check on it returns zero against a label that says otherwise. Nothing is wrong with the label. For drinks, use the alcohol calorie calculator, which works from ABV and volume instead. The alcohol tracking guide covers rounds, shared bottles, and when an exact number is not worth chasing.
The full set of factors a label may use
4/4/9 covers the three nutrients most foods are made of, but it is a simplification of a longer list. In the EU and UK, Annex XIV of Regulation 1169/2011 sets the conversion factors a manufacturer must use:
| Nutrient | kJ per gram | kcal per gram |
|---|---|---|
| Fat | 37 | 9 |
| Carbohydrate, except polyols | 17 | 4 |
| Protein | 17 | 4 |
| Alcohol (ethanol) | 29 | 7 |
| Polyols | 10 | 2.4 |
| Fibre | 8 | 2 |
| Erythritol | 0 | 0 |
This is the usual reason a 4/4/9 check disagrees with a printed label on the products where people notice it most. Sugar-free confectionery, protein bars and low-sugar drinks are built on polyols and fibre, and counting those at 4 instead of 2.4 or 2 inflates your total well above what the label declares. Erythritol at zero is the extreme case: it contributes grams to the carbohydrate figure and no energy at all.
If polyols and fibre are the part you are trying to untangle, the net carb calculator handles them separately, and it also covers the fact that the US and EU treat fibre differently in the carbohydrate figure.
The conversion factors are those set out in Annex XIV of Regulation (EU) No 1169/2011, which applies in the EU and was retained in UK law. US Nutrition Facts calories are declared under FDA labelling rules, which handle fibre differently.
Use the result as a check
The comparison tells you the size and direction of the difference. It does not declare the estimate or the label wrong. Keep the printed values for a packaged food unless you find a clear serving or data error.
Need to resize the entire meal? Use the portion macro scaler.