From a calorie target to grams: the macro-split arithmetic

A calorie target on its own doesn't tell you what to eat. Splitting it into grams of protein, carbohydrate and fat — the three "macros" — turns one number into a shopping list. The conversion is the same four steps no matter what percentages you're aiming for.

The method

Protein and carbohydrate both supply about 4 kcal per gram; fat supplies about 9 kcal per gram. These are the standard Atwater values. To go from a calorie target and a percentage split to grams:

1. calories from macro = total calories × that macro's percent ÷ 100
2. grams = calories from macro ÷ (4 or 9)

Protein and carbs both divide by 4; fat divides by 9, because fat is more energy-dense per gram. The three percentages don't have to be exactly 30/40/30 or any other round split — whatever you enter, the same two steps convert it to grams, though the percentages should sum to 100 or the resulting grams won't fully account for the calorie target.

A worked example

Target: 1,900 kcal/day, split 35% protein, 40% carbohydrate, 25% fat.

1. Protein calories: 1,900 × 35 ÷ 100 = 665 kcal. Grams: 665 ÷ 4 = 166.25 g.
2. Carb calories: 1,900 × 40 ÷ 100 = 760 kcal. Grams: 760 ÷ 4 = 190 g.
3. Fat calories: 1,900 × 25 ÷ 100 = 475 kcal. Grams: 475 ÷ 9 = 52.78 g.

Check it: 665 + 760 + 475 = 1,900 kcal, which matches the original target — the percentages summed to 100, so the three macro-calorie figures add back up exactly. In grams, that's about 166 g protein, 190 g carbs, 53 g fat per day.

What this doesn't include

This is unit conversion, not nutrition advice — it doesn't recommend a split, account for fiber, alcohol, or micronutrients, or adjust for training day versus rest day. The 4/9 kcal-per-gram values are standard averages; the actual energy your body extracts from a given food varies slightly with its source and how it's prepared. Whether a given calorie target and split fits your goals and health is a separate question from this arithmetic. Informational only, not dietary or medical advice.

Run your own numbers

The free Macro Split tool takes a calorie target and three percentages and returns grams of protein, carbs and fat instantly, entirely on your device.