Enter a daily calorie target and a protein/carb/fat percentage split to calculate grams of each macronutrient.

How to Use the Macro Calculator

Start with the calorie target, then adjust the three percentage fields — the gram totals update as you go, and an error appears if the percentages stop adding to 100.

Total calories is one number; how those calories are split between protein, carbohydrate, and fat is a separate decision entirely, and it's the one this calculator handles — turning a percentage split into actual grams to plan meals around.

Protein (g) = (Calories × Protein %) ÷ 4
Carbs (g)   = (Calories × Carb %) ÷ 4
Fat (g)     = (Calories × Fat %) ÷ 9

Protein and carbohydrate both provide 4 calories per gram; fat provides 9 — the Atwater system of calorie-per-gram values, developed by chemist Wilbur Atwater in the 1890s and still the basis for nutrition-label calorie counts today. It's why the same percentage of calories translates to a much smaller gram figure for fat than for the other two. There's no single "correct" split enforced here; a 40/30/30 protein/carb/fat plan and a 30/40/30 one are both valid depending on the goal, which is why this tool takes the percentages as input rather than assuming one.

The three percentages need to add to 100 — this calculator checks that and flags it if they don't, rather than silently normalizing numbers that don't actually represent the plan entered.

A math tool, not a nutrition plan. This calculator converts percentages to grams — it doesn't recommend what split is right for you. A registered dietitian can help translate goals and health context into an actual target.