Macros explained: turning a calorie target into grams

A macro split is usually written as three percentages — 30/40/30, 40/35/25 — but you cannot eat a percentage. Turning it into grams takes one fact: protein and carbohydrate carry 4 calories per gram, fat carries 9. Everything else on this page follows from that.

The calculation, once

Take the percentage of your daily calories, then divide by the calories per gram of that macro. On a 2,400 kcal day with a balanced 30/40/30 split:

Protein = 2,400 × 0.30 ÷ 4 = 180 g. Carbohydrate = 2,400 × 0.40 ÷ 4 = 240 g. Fat = 2,400 × 0.30 ÷ 9 = 80 g.

Notice fat: the same 30% buys you 80 g rather than 180 g, because each gram is worth more than twice as much. This is why a "high fat" split looks so small on the plate and why fat percentages move a diet further than the number suggests.

What the standard splits actually come out as

The macro calculator ships five presets. At 2,400 kcal they land here:

Balanced (30/40/30) — 180 g protein, 240 g carbs, 80 g fat.
High protein (40/35/25) — 240 g, 210 g, 67 g.
Low carb (35/20/45) — 210 g, 120 g, 120 g.
Keto (25/5/70) — 150 g, 30 g, 187 g.
Endurance (20/55/25) — 120 g, 330 g, 67 g.

Read down the fat column and the point of the 9 becomes obvious: keto's 70% is 187 g, while endurance's 25% is 67 g. Read across keto and note that 30 g of carbohydrate is roughly one slice of bread and a piece of fruit for the entire day.

Set protein first, split the rest

Percentages are a convenient way to write a plan down, but they are the wrong way to build one. Protein requirement scales with body weight, not with calorie intake — so a percentage-first plan quietly gives a heavier person less protein per kilo on a cut, exactly when they need more.

Work the other way. Fix protein in grams per kilogram, convert to calories, and split whatever is left between carbohydrate and fat according to how you train and what you actually enjoy eating. At 78 kg, that 180 g works out at 2.31 g/kg — comfortably in the range used for preserving muscle in a deficit, and well above EFSA's population reference intake of 0.83 g/kg/day, which is a floor for adequacy rather than a target for training.

The number that has to be right first

All of this is a division of your calorie target, so the split is only as good as the target. Get that from TDEE — your BMR multiplied by an activity factor between 1.2 for sedentary and 1.9 for heavy training — and then apply a deliberate surplus or deficit. A perfect 40/35/25 around the wrong calorie number is a precisely specified mistake.

Limits worth knowing

The 4/4/9 figures are Atwater averages, not measured values for a specific food: fibre yields less, alcohol adds a fourth number at 7 kcal per gram that no split accounts for, and absorption varies. Macros are a planning grid, not a metabolic ledger. Consistency over a week beats precision on a Tuesday.

Reading a food label into your split

Macros only work if the numbers going in are right, and labels have two traps. The first is per-100g versus per-serving: the large-print figures on the front are usually per serving, and the serving is often smaller than the portion anyone actually eats. The second is that stated protein includes everything nitrogenous in the product, so a "high protein" snack built on gelatine or collagen contributes far less usable protein than the label implies.

Weighing food for two or three days is the fastest way to calibrate. Most people discover their estimates are out by 20–30% on calorie-dense items — oils, nut butters, cheese, cereal — and close to accurate on everything else. You do not need to weigh forever; you need to weigh long enough to know what your normal portions actually are.

Timing matters less than the daily total

The evidence for meal timing is much weaker than the internet suggests. Total daily protein has a clear effect on retaining muscle in a deficit; spreading it across three or four meals of roughly 0.3–0.4 g per kilogram each is a mild additional benefit, and precise windows around training are close to irrelevant for anyone not competing. Carbohydrate placement is worth considering only for genuine performance reasons: eating most of it around the session you care about tends to make that session feel better.

What does matter is consistency across weeks. Set the target once from your energy needs — the TDEE calculator for the total and the protein calculator for the floor — then hold it long enough to read a trend. Two weeks of average intake against two weeks of average weight tells you far more than any single day, and if the trend is flat, adjust the calories rather than reshuffling the split.