Macro Calculator
Split a daily calorie target into grams of protein, carbs and fat using a preset or custom ratio, based on the 4/4/9 kcal-per-gram Atwater factors.
165 g
660 kcal/day
220 g
880 kcal/day
73 g
660 kcal/day
Grams are derived from the Atwater factors: protein and carbohydrate provide 4 kcal per gram, fat provides 9. A common protein-first approach is to fix protein at 1.6–2.2 g per kg of body weight, then divide the remaining calories between carbs and fat to taste. These numbers are a starting point, not medical or dietary advice.
Turning a calorie target into protein, carbs and fat
"Macros" are the three energy-providing nutrients: protein, carbohydrate and fat. Each has a roughly fixed energy density — the Atwater factors of 4, 4 and 9 kilocalories per gram. Once you know how many calories you want per day and what percentage should come from each macro, converting to grams is arithmetic: multiply calories by the percentage, divide by that macro’s calories-per-gram.
Calories decide whether weight goes up or down; macros shape what happens within that calorie level. Adequate protein preserves muscle when you are in a deficit and supports recovery from training. Carbohydrate fuels higher-intensity exercise and is the easiest lever to move up or down. Dietary fat supports hormone production and satiety, with a common floor around 0.5–0.8 g per kg of body weight.
The presets here cover the usual starting points: balanced (about 30/40/30), high-protein (40/40/20), low-carb (40/20/40) and keto (25/5/70). None is magic. Adherence beats theoretical optimality, so pick the split that fits how you like to eat and train. A widely used method is to set protein first at 1.6–2.2 g per kg of body weight, then divide the remaining calories between carbs and fat by preference.
Treat the output as a target range, not a prescription. Day-to-day variation is normal and fine; the weekly average is what matters. Food quality, fibre, micronutrients, sleep and training consistency all influence results and are not captured by a macro ratio. This is a general fitness tool — therapeutic diets for medical conditions must come from a qualified dietitian or physician.
All calculations run in your browser. Nothing you enter is stored or sent anywhere.
Key formulas (reference)
kcal from macro = calorieTarget × (macro% ÷ 100) grams of protein = kcalₚ ÷ 4 grams of carbs = kcal_c ÷ 4 grams of fat = kcal_f ÷ 9 (custom percentages are normalised so protein% + carb% + fat% = 100)
Related tools
These free tools pair well with this page — open them in a new tab to finish your workflow.
Frequently Asked Questions
How are grams calculated from calories?
Using the Atwater factors: protein and carbohydrate each provide about 4 kilocalories per gram, and fat provides about 9. The calculator multiplies your calorie target by each macro’s percentage, then divides by that macro’s calories-per-gram to get grams.
What macro split should I use?
For general health, a balanced split (roughly 30% protein, 40% carbs, 30% fat) works for most people. Higher protein (35–40%) helps preserve muscle in a calorie deficit. Low-carb and keto shift calories toward fat and are a preference, not a requirement. The best split is one you can sustain.
How much protein do I actually need?
Research on active people and those losing weight generally supports 1.6–2.2 grams of protein per kilogram of body weight per day (about 0.7–1.0 g per pound). A common method is to set protein by body weight first, then divide the remaining calories between carbs and fat.
Where do I get my calorie target?
Use the Calorie Calculator (goal-based) or the TDEE Calculator (maintenance) to estimate it, then enter that number here. Macros are a way of dividing up a calorie budget — they do not set the budget.
Do the percentages have to add up to 100?
For a custom split, if they do not total 100 the calculator normalises them proportionally so the grams still match your calorie target. The presets are already balanced to 100%.
Does hitting my macros guarantee results?
No. Total calories drive weight change; macros influence body composition, satiety and training performance within that calorie level. Food quality, fibre, micronutrients, sleep and consistency all matter and are not captured by a macro split.
Is this suitable for medical or clinical diets?
No. This is a general fitness tool. Therapeutic diets — for diabetes, kidney disease, or a medically supervised ketogenic protocol — must be set by a qualified dietitian or physician.