Macro Calculator

This is a unit conversion, not a nutrition plan. You supply a daily calorie figure and pick a percentage split; the tool divides the calories between protein, carbohydrate and fat and converts each share into grams. The arithmetic is exact. Whether the split suits you is a separate question the calculator has no opinion on.

Atwater factors do the conversion

Each macronutrient carries a conventional energy value, the Atwater factors used on food labels worldwide:

protein        4 kcal per gram
carbohydrate   4 kcal per gram
fat            9 kcal per gram

grams = (daily calories x percentage) / kcal per gram

At 2,000 kcal on the balanced 40/30/30 split, carbohydrate takes 40% — that is 800 kcal, and 800 / 4 = 200 g. Protein takes 30%, so 600 / 4 = 150 g. Fat takes the remaining 30%, but at 9 kcal per gram that is 600 / 9 = 67 g.

The fat figure surprises people every time. It is not an error and nothing has been rounded away: fat is more than twice as energy dense as the other two, so the same share of calories buys less than half the grams. The keto preset makes this vivid — at 2,000 kcal and a 5/25/70 split you get 25 g of carbohydrate, 125 g of protein and 156 g of fat.

The splits are conventions

Forty/thirty/thirty is a convention that became popular through 1990s diet books; the high-protein and ketogenic presets are conventions too. None of them is a physiological requirement, and the body does not need any exact gram figure the calculator prints. What it needs is enough protein to maintain tissue, enough fat for fat-soluble vitamins and hormone synthesis, and enough total energy — the proportions above those floors are largely a matter of preference and adherence.

Randomised comparisons of diets matched for calories and protein tend to find similar fat-loss outcomes across quite different carbohydrate and fat proportions. Total energy drives weight change. The split mainly determines whether the process feels tolerable, and the best ratio is the one you will still be following in three months.

The ketogenic preset deserves an extra sentence. Very low carbohydrate intake is a therapeutic intervention in some contexts, and it interacts with medication — insulin and SGLT2 inhibitors in particular — in ways that need supervision. It is not simply another slider position.

What this model leaves out

Two energy sources are not represented at all. Dietary fibre is partially fermented rather than fully absorbed and is assigned about 2 kcal per gram under EU labelling rules; here it is counted at the full carbohydrate value of 4. Alcohol supplies 7 kcal per gram and has no macronutrient category, so any drinks you have are simply absent from the split while still counting toward the calories.

The Atwater factors themselves are averages across food types rather than exact values for any particular meal, and absorption varies with processing and preparation. That is a small imprecision compared with the error in estimating your calorie needs in the first place, but it is worth knowing the label figures are approximations.

Nothing here checks that your calorie target is sensible. If the number you typed came from a guess, the grams will be a precise division of a guess. The calorie calculator estimates a maintenance figure from your measurements and activity level, which is a better starting point, and the protein intake calculator sets protein from body weight and training goal rather than as a percentage — often the more useful way round, since protein need scales with body size rather than with how much you happen to be eating.

If you want to run other kinds of ratio and percentage arithmetic, the general calculators section covers that ground.

The conversion is performed in your browser, no figures are transmitted, and your own browser may keep the last values you entered. Nobody with nutrition or medical credentials has reviewed this page.