Macros — protein, carbohydrate and fat — are the energy-providing nutrients. A macro calculator turns a calorie target into grams of each by applying their fixed energy densities: protein and carbohydrate give 4 calories per gram, fat gives 9. For any macro, grams = calories × its percentage ÷ its calories-per-gram. Choosing a split (the percentages, which must total 100%) shapes the diet toward a goal — more protein for muscle, fewer carbs for some appetite preferences — while the calorie total still drives weight change.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: Atwater energy factors (4/4/9). Not medical advice.
The macro equations
Each macro's share of calories is the calorie total times its percentage. Dividing by the energy density — 4 for protein and carbohydrate, 9 for fat — converts those calories into grams. Because fat packs more than double the energy per gram, an equal calorie share becomes far fewer grams of fat than of protein or carbs. The percentages must sum to 100%, so the split is a way of dividing the same calorie budget three ways.
Worked example — 2,000 calories, balanced split
Scenario: a 2,000-calorie day at a balanced 30% protein / 40% carb / 30% fat.
That is 150 g of protein, 200 g of carbohydrate and about 66.7 g of fat — which checks back to 600 + 800 + 600 = 2,000 calories. Re-weight the split and the grams shift: a high-protein 40/40/20 gives 200 g protein, 200 g carb and ~44 g fat, while a low-carb 40/20/40 gives 200 g protein, 100 g carb and ~89 g fat. The right split is personal; a common protein guideline for active people is about 1.6–2.2 g per kg of body weight.
Frequently Asked Questions
Protein, carbs and fat. Protein & carbs = 4 cal/g; fat = 9 cal/g. Splits total 100%.
grams = cal × percent / cal-per-gram. 2000 at 30/40/30 → 150 g P, 200 g C, 66.7 g F.
Balanced 30/40/30, high-protein 40/40/20, low-carb 40/20/40 — depends on goals.
Fat is 9 cal/g, so the same calories = fewer grams. 600 cal = 150 g protein but ~67 g fat.
No — an educational planning tool. For a personalised plan, see a registered dietitian.