Macros are the three nutrients that carry calories — protein, fat and carbohydrate — and "counting macros" means tracking the grams of each rather than the calorie total alone. The word is short for macronutrients: nutrients needed in gram amounts each day, as opposed to micronutrients (vitamins and minerals), which are needed in milligrams or micrograms.

This article explains what each macro is, how many calories a gram of it carries, why the macro calculator works in grams, and the exact order in which a target is built.

The three macros (plus alcohol)

Protein is made of amino acids, the building blocks of muscle and of almost every working part in the body. Meat, fish, eggs, dairy, soy, legumes and grains all contain it in different amounts.

Fat is the most energy-dense macro. Oils, butter, nuts, seeds, oily fish, egg yolk and the fat in meat and dairy are the main sources.

Carbohydrate covers starches (bread, rice, potatoes, oats), sugars (fruit, milk, table sugar) and fibre (the parts of plants that are not digested in the small intestine).

Alcohol is not a nutrient, but it carries calories, so a macro tracker has to account for it somewhere. It is listed here because it is the fourth energy source on the label conversion tables.1

In plain terms: protein builds, fat and carbohydrate mostly fuel, and alcohol is extra energy that has to be counted even though it is not food.

Calories per gram

The energy factors used on food labels are the Atwater general factors, published in FAO's reference on food energy conversion:1

Energy sourcekcal per gramkJ per gram100 g supplies
Protein417400 kcal
Carbohydrate417400 kcal
Fat937900 kcal
Alcohol729700 kcal
Dietary fibre28200 kcal

Two things follow from the table. A gram of fat carries more than twice the energy of a gram of protein or carbohydrate, which is why fat grams look small next to carb grams even when the calories are similar. And the factors are averages: the true energy of a specific food's protein or carbohydrate varies around them, which is the subject of why macros don't add up to calories.

Why grams, not percentages

A percentage split — "40/30/30" — says nothing until you know the calorie total. 30% protein at 1,600 kcal is 120 g; at 2,800 kcal it is 210 g. The body does not respond to a percentage. It responds to the grams of protein relative to body weight and to the calorie total relative to expenditure.

That is why the MacroDiet formula never starts from a ratio. Protein is set in grams per kilogram of body weight, fat has a floor in grams per kilogram, and only the leftover is divided. Percentages are a way of describing the result afterwards.

How targets are set — energy, then protein, then fat, then carbs

The order is fixed and every step depends on the one before it. This is the exact sequence the macro calculator runs:

  1. Energy. BMR from the Mifflin-St Jeor equation, multiplied by an activity factor, adjusted for the goal (lose, maintain, gain) with a cap of 35% of TDEE on any deficit or surplus and a calorie floor on the way down.
  2. Protein. Body weight × a tier of 1.2, 1.6, 2.0 or 2.4 g/kg, plus 0.2 g/kg on a losing goal, capped so protein never exceeds 50% of calories.
  3. Fat. A share of the calories left after protein — 35% on the balanced style, 20% low-fat, 50% low-carb — never below the floor of max(0.6 g/kg, 20% of calories).
  4. Carbohydrate. Everything that remains, divided by 4. On keto the order of the last two steps flips: carbs are fixed at 30 g and fat takes the remainder.
BalancedP 150 gF 54 gC 229 gLow fatP 150 gF 45 gC 249 gfloor 31 → 45 gLow carbP 150 gF 78 gC 175 gKetoP 150 gF 142 gC 30 gProteinFatCarbsBars are proportional to calories (4 · 9 · 4 kcal/g); labels are grams.
Fig. The four diet styles at 2,000 kcal for a 75 kg example with protein held at 150 g (2 g/kg). Fat takes a fixed share of the calories left after protein — 35% balanced, 20% low fat, 50% low carb — and carbohydrate fills the rest; keto fixes carbs at 30 g and lets fat balance. The fat floor (the higher of 0.6 g/kg and 20% of calories, here 45 g) lifts the low-fat split. Computed from the algorithm's constants; the split describes what the formula sets, not what anyone should eat.

A worked example, reproducible on the calculator: an 80 kg person at a 2,200 kcal maintenance target, moderate protein tier, balanced style.

StepArithmeticResult
Protein80 × 1.6128 g = 512 kcal
Remaining2,200 − 5121,688 kcal
Fat1,688 × 0.35 ÷ 966 g = 594 kcal
Fat floor checkmax(80 × 0.6, 2,200 × 0.2 ÷ 9) = max(48, 49)49 g — not binding
Carbohydrate(2,200 − 512 − 594) ÷ 4274 g

In plain terms: calories are decided first, protein is protected, fat gets a floor, and carbohydrate is the flexible remainder that absorbs whatever changes.

The short version

Macros are protein, fat and carbohydrate — the nutrients that carry calories, at 4, 9 and 4 kcal/g, with alcohol at 7. Targets are set in grams because grams, not percentages, are what the body sees. The MacroDiet order is energy → protein → fat → carbs, and each later step is the remainder of the earlier ones. The protein, fat and carbohydrate articles take each step in turn.

Educational overview only — not medical advice. Zyra is a training and nutrition tracking tool; the numbers here are the algorithm's rules and published reference values, not an individual prescription.