Macro Calculator
Split a daily calorie target into protein, carbs and fat by percentage, or pin protein first and divide the rest. Shows grams, calories and grams per kilo side by side.
About this tool
A macro split looks like simple arithmetic until you try to make the numbers agree. Fat supplies nine calories per gram, while protein and carbohydrate supply four each. A split of 30% protein, 40% carbohydrate and 30% fat on a 2,200 calorie target therefore works out to 165 g, 220 g and 73 g: the fat gram count is far smaller than the other two because each fat gram is worth more than twice as much.
The second thing that catches people is that a percentage split and a grams-per-kilo target are not two ways of saying the same thing. If you weigh 75 kg and eat 165 g of protein, you are eating 2.2 g per kilo. If instead you aim for 1.8 g per kilo, you land on 135 g, which is only 24.5% of a 2,200 calorie day. Both figures are correct, but they answer different questions, and only one of them is stable when your calories change. Raise the calorie target without raising protein and the percentage falls; keep the grams per kilo and the percentage moves as your weight moves.
This calculator keeps both views on the same screen. Whatever mode you use, it reports grams, the calories those grams carry, the share of the total and the grams per kilo of body weight. That way you can see when a headline percentage is quietly asking you to eat far more or far less protein than the grams-per-kilo figure would suggest.
Why protein and carbs are 4 kcal per gram but fat is 9
The four and nine are Atwater factors, the average amount of usable energy the body extracts from each gram. Fat is more than twice as energy-dense, which is why a fat target in grams always looks small next to a carbohydrate target of the same calorie share.
The numbers come from measuring how much of each macronutrient is actually absorbed and oxidised, not from burning it in a bomb calorimeter. Protein is listed at four calories per gram even though it yields slightly more when burned, because the body spends energy handling the nitrogen and does not extract all of it. Carbohydrate sits at four, and fat at nine. Alcohol would be seven, and fibre is usually counted at about two, but neither is part of the three-way split here.
The practical consequence is that gram counts are not comparable across the three macros. Seeing "165 g protein, 220 g carbs, 73 g fat" and assuming the fat share is the smallest is the standard mistake: in calories, all three are near a third. Whenever you compare a macro plan, convert to calories first, or the split will look lopsided when it is not.
The identity that has to hold is 4P + 4C + 9F = total calories. If you build a plan and those three terms do not add up to your target, one of the inputs is wrong. This calculator uses that identity as its main consistency check, and the rounded totals it displays are computed from it rather than stored separately.
Percentage of calories versus grams per kilo
A percentage split fixes the shape of the diet; grams per kilo fixes the protein intake to your body. At 2,200 calories, 30% protein and 1.8 g/kg on a 75 kg body give 165 g and 135 g respectively — a 30 g gap that neither view reveals on its own.
The two views drift apart whenever calories or body weight change. Suppose you cut from 2,200 to 1,800 calories and keep the 30% protein share. Protein drops from 165 g to 135 g, which on a 75 kg body is 1.8 g/kg instead of 2.2. Nothing about your body changed, but your protein intake fell by 18%. That is why plans written as percentages tend to lose protein during a cut, and it is the reason the protein-first mode exists.
Going the other way, a fixed grams-per-kilo target turns into a moving percentage. At 1.8 g/kg and 75 kg you eat 135 g of protein whether you are on 1,800 or 2,600 calories. On the lower target that is 30% of the day; on the higher one it is 20.8%. The absolute intake is stable and the share is not.
Neither is wrong. Percentages are easier to scale and easier to explain. Grams per kilo are easier to keep constant across a diet phase. What matters is knowing which one you are looking at, and the panel here always shows the other one alongside it so the conversion is never hidden.
What rounding does to the calories you actually eat
You weigh food in whole grams, so the plan you execute is the rounded one. Rounding can move the total by up to about nine calories, and the calculator shows that difference rather than hiding it behind an exact-looking total.
A 30% fat share of 2,200 calories is 660 kcal, which is 73.33 g. Nobody weighs 73.33 g, so the plan becomes 73 g, and 73 g of fat is 657 kcal. Add 165 g of protein at 660 kcal and 220 g of carbs at 880 kcal and the day comes to 2,197 kcal, three below the target. If you had rounded the fat up to 74 g the day would have come to 2,206. The error is small because the grams are large, but it is real and it has a direction.
The larger version of the same problem appears at low calorie targets. On a 1,200 calorie day, a 25% fat share is 33.3 g, and a single gram is worth 1.5% of that fat allowance. Rounding a fat target of 33.3 g to 33 changes the fat calories by 2.7%, which is enough to matter over a week. The smaller the target, the more a gram costs.
Because of this, every calorie figure on the results panel is computed from the rounded gram figure, not from the exact share. The three cards and the total therefore agree with each other, and the difference line tells you exactly how far the rounded plan sits from the target. A plan you can add up on a calculator is more useful than one that is exact on paper and impossible in a kitchen.
It does not answer how much you should eat
This page does one thing: given your rules — a calorie target, a protein percentage or grams per kilo — it returns grams of each macronutrient. Whether 2,200 kcal is right for you, or whether protein should be 1.6 or 2.2 g/kg, is outside what it answers.
The reason is practical: a calorie target follows from your training phase, your rate of weight change and possibly medical advice, none of which the tool knows. Supplying a default would invite readers to treat it as a recommendation.
Four, four and nine are the whole physics: protein and carbohydrate at 4 kcal per gram, fat at 9. Thirty grams of fat is therefore 270 kcal, not 120 — using 4 would understate fat by more than half, and the error propagates into the daily total.
Percentage mode and grams-per-kilo mode are not conversions of each other. The first fixes the calorie split; the second fixes protein in grams and distributes what remains to carbohydrate and fat. The same inputs give different answers in the two modes, which is not a bug but the answer to two different questions.
Rounding happens once, at the end: grams are computed first and rounded afterwards, never rounded and multiplied back as calories. Otherwise a 0.4 g difference accumulates into several kcal, and the page gives no clue which step produced it.
Frequently asked questions
Why does fat get so few grams compared with carbs?
Because a gram of fat carries nine calories and a gram of carbohydrate carries four. At the same share of total calories, fat weighs about 44% of what carbohydrate would weigh. A 30% fat share on 2,200 calories is 660 kcal, which is 73 g; a 30% carbohydrate share would be 165 g. The calorie totals are identical, the gram totals are not.
Should I use percentages or grams per kilo?
They answer different questions. Percentages describe the shape of the diet and scale automatically with your calorie target, which is convenient when calories change often. Grams per kilo tie protein to your body weight, which keeps the intake stable when you change calories and is the way most training guidance is written. A practical middle ground is to set protein by grams per kilo, then split the remaining calories between carbs and fat — which is exactly what the protein-first mode does.
Why does the rounded total not match my calorie target?
Because whole grams cannot represent a fraction. A 30% fat share of 2,200 calories is 73.33 g, which rounds to 73 g, and 73 g of fat is 657 kcal rather than 660. Across three macros the rounded total typically lands within about nine calories of the target in either direction. The difference is shown explicitly so the numbers on the page always add up, rather than looking like an error.
What does "carbs take the rest" mean?
In protein-first mode, protein is fixed by your body weight and grams per kilo. Whatever calories remain after protein are divided between carbohydrate and fat. The slider sets what fraction of those remaining calories goes to carbohydrate; the rest goes to fat. Setting it to 100 gives an almost fat-free split, and setting it to 0 gives a very low-carb split — the calculator will produce either, because it is a calculator.
Are the reference ranges medical advice?
No. The ranges shown next to the grams-per-kilo figures are commonly cited figures from sports nutrition literature, presented as a comparison point only. They do not account for medical conditions, medication, pregnancy, age or any individual factor, and this tool does not diagnose or prescribe. If you need a plan for a specific condition, that is a conversation with a clinician or a registered dietitian.
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