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Macronutrient Split Calculator

Split a daily calorie target into grams of protein, carbs, and fat from your own target percentages.

Protein
150 g (600 kcal)
Carbohydrates
200 g (800 kcal)
Fat
67 g (600 kcal)

How it works

This splits your daily calorie target across the three macronutrients using the percentages you choose, then converts each calorie share into grams using the Atwater general factors — the standard nutritional-science energy density of each macronutrient: 4 kcal per gram of protein, 4 kcal per gram of carbohydrate, and 9 kcal per gram of fat. These conversion factors are fixed physical constants (the same ones on every nutrition label), not a fact that changes over time.

Grams for each macro are simply (calories × that macro's percentage ÷ 100) ÷ its kcal-per-gram factor. Fat's higher factor (9 vs. 4) means the same number of calories always works out to fewer grams of fat than grams of protein or carbs.

Your three percentages must add up to 100% — this calculator doesn't pick a diet split for you, since there's no single 'correct' macro ratio; it just does the arithmetic once you've decided on one.

FAQ

Why does fat come out to fewer grams than protein or carbs at the same percentage?

Because fat has more than double the energy density — 9 kcal per gram versus 4 for protein and carbs — so the same calorie allotment converts to roughly 4/9 as many grams of fat as it would grams of protein or carbs.

Where do the 4/4/9 numbers come from?

They're the Atwater general factors, derived from the average energy each macronutrient releases when metabolized, and they're what's used to calculate the calorie counts on nutrition labels — this calculator just runs that same conversion in reverse, from calories back to grams.

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