From calories to grams
Food energy comes from three macronutrients. Each gram of carbohydrate or protein provides about 4 kilocalories and each gram of fat about 9 — the Atwater factors used on every U.S. Nutrition Facts label. Choosing a split means deciding what share of your calories each macro supplies; dividing those calories by the energy per gram gives a gram target you can track in a food log.
The formulas
Carbs (g) = calories × carb % / 4 Protein (g) = calories × protein % / 4 Fat (g) = calories × fat % / 9 Protein per kg = protein g / body weight (kg)
Acceptable Macronutrient Distribution Ranges (adults)
| Macronutrient | % of calories | kcal per gram |
|---|---|---|
| Carbohydrate | 45–65% | 4 |
| Protein | 10–35% | 4 |
| Fat | 20–35% | 9 |
Worked example
2,200 kcal on a balanced 50 / 20 / 30 split: carbs 2,200 × 0.50 / 4 = 275 g; protein 2,200 × 0.20 / 4 = 110 g; fat 2,200 × 0.30 / 9 = 73 g.
For someone weighing 170 lb (77.1 kg), 110 g of protein is 1.43 g/kg — above the 0.8 g/kg RDA (62 g) and inside the 1.2–2.0 g/kg range often used by active people.
Limitations
- Fiber is counted with carbohydrate here; it provides fewer usable calories (about 2 kcal/g), so labels can differ slightly.
- The ranges are for healthy adults. Kidney disease, diabetes, pregnancy and other conditions can change protein and carbohydrate needs.
- Gram targets are rounded to the nearest gram.
Sources: Institute of Medicine (National Academies), Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005); USDA, Dietary Guidelines for Americans; Jäger R et al., "ISSN Position Stand: protein and exercise," J Int Soc Sports Nutr 2017;14:20.
Frequently asked questions
How many calories should I enter?
Your daily target. If you don't know it, use the calorie calculator first: it estimates maintenance calories with the Mifflin-St Jeor equation and adjusts for weight loss or gain. Then come back with that number.
What macro split is best?
There is no single best split. The National Academies' Acceptable Macronutrient Distribution Ranges for adults are 45–65% of calories from carbohydrate, 10–35% from protein and 20–35% from fat; diets inside those ranges are linked with lower chronic-disease risk. Within them, the right mix is the one you can stick to. Studies comparing low-carb and low-fat diets with equal calories find similar weight loss.
How much protein do I need?
The RDA for adults is 0.8 g per kilogram of body weight per day — about 0.36 g per pound, or 62 g for a 170 lb person. That is a minimum to avoid deficiency. Athletes and people losing weight who want to keep muscle often aim for 1.2–2.0 g/kg, a range supported by sports-nutrition position statements.
Why are fat grams lower than carb grams for the same percentage?
Fat has 9 calories per gram while carbohydrate and protein have 4. So 30% of 2,200 calories is 660 calories, which is 165 g of carbohydrate or protein but only 73 g of fat.
Does alcohol count?
Alcohol supplies about 7 calories per gram and isn't a macronutrient you need. If you drink, those calories come out of your daily total, leaving less room for the three macros.
This calculator is for general information and screening only and is not medical advice. Talk to a doctor or registered dietitian before making changes based on the result, especially if you are pregnant, under 18, or managing a health condition.