Calories per gram of protein, carbs, fat and alcohol
Food energy comes from four sources. Each gram supplies a fixed, rounded number of calories, known as the Atwater general factors:
| Nutrient | Calories per gram | Kilojoules per gram |
|---|---|---|
| Protein | 4 | 17 |
| Carbohydrate | 4 | 17 |
| Fat | 9 | 37 |
| Alcohol | 7 | 29 |
So 1 gram of protein has 4 calories, and 1 gram of fat has 9 calories, more than twice as much. Water, vitamins and minerals provide no calories.
How it's calculated
Calories = protein g × 4 + carbohydrate g × 4 + fat g × 9 + alcohol g × 7
Share from each = its calories ÷ total calories × 100
Share from each = its calories ÷ total calories × 100
Worked example
A day with 150 g of protein, 200 g of carbohydrate and 60 g of fat:
150 × 4 = 600 · 200 × 4 = 800 · 60 × 9 = 540
Total = 600 + 800 + 540 = 1,940 calories
Total = 600 + 800 + 540 = 1,940 calories
Protein supplies 600 ÷ 1,940 = 30.9% of the calories, carbs 41.2% and fat 27.8%. A US standard drink contains about 14 grams of pure alcohol, which adds about 14 × 7 = 98 calories before any mixer.
Limitations
- 4, 4, 9 and 7 are rounded averages. The exact energy varies a little between foods, so a food company's total can differ slightly from this calculation.
- Nutrition labels round both calories and grams, so adding up a label's grams may not match its calories exactly.
- This adds up calories. It doesn't say how much of each nutrient you need. For targets, use the macro calculator or the protein calculator.
New to macros? Read what are macros.
Sources
- NIDDK health dictionary: calorie — 4 calories per gram of carbohydrate and protein, 9 for fat, 7 for alcohol.
- FAO: Food energy, methods of analysis and conversion factors (2003), chapter 3 — 1 kcal = 4.184 kJ, and the Atwater factors 4, 4, 9 and 7.
- MedlinePlus (NIH): Alcohol and diet — about 7 calories per gram.
- NIAAA (NIH): What is a standard drink? — about 14 grams of pure alcohol.
- MedlinePlus (NIH): Dietary fats explained