Macro Calculator

This is a unit conversion, not a nutrition plan. You give it a daily calorie figure and pick a percentage split, and 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, and the calculator has no opinion on it.

Atwater factors do the conversion

Each macronutrient has a conventional energy value. These are 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's 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's 600 / 9 = 67 g.

People are always surprised by the fat figure. It's correct, 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. You can see this clearly with the keto preset. 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 became popular through 1990s diet books, and the high-protein and ketogenic presets are conventions too. None of them is a physiological requirement, and your body doesn't need any exact gram figure the calculator prints. It needs enough protein to maintain tissue, enough fat for fat-soluble vitamins and hormone synthesis, and enough total energy. Above those floors, the proportions are largely down to preference and what you can stick with.

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 mostly decides whether the process feels bearable, and the best ratio is the one you'll still be following in three months.

The ketogenic preset needs an extra word of caution. Very low carbohydrate intake is used as a therapeutic intervention in some contexts, and it interacts with medication (insulin and SGLT2 inhibitors in particular) in ways that need medical supervision. Don't treat it as just another slider position.

What this model leaves out

Two energy sources aren't represented at all. Dietary fibre is only partly absorbed, with some of it fermented in the gut, and EU labelling rules assign it about 2 kcal per gram. Here it's 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 missing from the split while still counting toward the calories.

The Atwater factors themselves are averages across food types, not exact values for any particular meal, and absorption varies with processing and preparation. That's a small imprecision next to the error in estimating your calorie needs in the first place, but you should know the label figures are approximations.

The tool doesn't check that your calorie target is sensible. If you guessed the number you typed, the grams will be a precise division of a guess. The calorie calculator estimates a maintenance figure from your measurements and activity level, which gives you a better starting point. The protein intake calculator sets protein from body weight and training goal instead of as a percentage. That's often the more useful way round, since protein need scales with body size and not 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 runs 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.