Nutrition guide
How To Calculate Macros
Macro calculation starts with an energy estimate, then assigns protein and fat before distributing remaining energy to carbohydrate and fat according to the plan.
Updated 16 October 2026 • Reviewed by Tools by Layna Editorial Team • General information only
Convert an energy target into grams
A macro calculation needs an energy total and a defined allocation method. Percentages alone are incomplete: convert them into grams and check that all allocations fit the same total. A calculated split is a starting framework, not evidence that the diet suits a particular person.
For simple kcal arithmetic, protein and carbohydrate contribute about 4 kcal per gram and fat about 9 kcal per gram. Food-label energy can differ because of rounding, fibre and other energy-containing components.
Worked example: a complete split that adds up
At an illustrative 2,000 kcal, a 25% protein, 45% carbohydrate and 30% fat split totals 100%. Protein is 500 ÷ 4 = 125 g; carbohydrate is 900 ÷ 4 = 225 g; fat is 600 ÷ 9 = 66.7 g. These numbers demonstrate conversion, not a recommended meal plan.
| Macro | Share | Energy | Grams before rounding |
|---|---|---|---|
| Protein | 25% | 500 kcal | 125 g |
| Carbohydrate | 45% | 900 kcal | 225 g |
| Fat | 30% | 600 kcal | 66.7 g |
How this site’s macro calculator works
The Macro Calculator uses a different preset method. It estimates resting energy from age, sex, height and weight, multiplies by the selected activity factor, then applies the goal adjustment: −350 kcal for loss, +250 kcal for gain, or no adjustment for maintenance.
Its protein presets are 1.6 g/kg for maintenance, 1.8 g/kg for loss and 2.0 g/kg for gain. Fat receives 28% of the calculated energy; carbohydrate receives the energy left after protein and fat. The tool does not offer a preferred-split selector. These are implementation assumptions, not official population recommendations.
For example, if estimated maintenance is 2,400 kcal, weight is 70 kg and maintenance is selected, protein is 112 g, fat is 74.7 g and carbohydrate is 320 g before display rounding. The energy check is 448 + 672 + 1,280 = 2,400 kcal.
Check the assumptions before using the output
Try a realistic neighbouring activity estimate and compare the difference. An activity category is a major source of uncertainty; more decimal places cannot resolve it. Check whether the resulting grams fit normal meals, food preferences and training demands.
Do not combine the upper end of separate macro ranges without checking the total. If protein and fat already consume the full energy allowance, a negative carbohydrate result indicates incompatible assumptions and should not become a target. Health conditions, pregnancy and eating-disorder risk need individual advice.
Frequently asked questions
Can I choose any three macro percentages?
They must add to 100% when allocating the whole energy total. Separately listed ranges are alternatives to be combined coherently, not three independent maxima.
Is the example split the same as the calculator preset?
No. The 25/45/30 example teaches percentage-to-gram conversion. The calculator sets protein by body weight, fat at 28% of energy and carbohydrate from the remainder.
Why did the macro result change after selecting another activity level?
The activity factor changes the estimated maintenance energy. That changes available energy for fat and carbohydrate even when the body-weight-based protein preset stays the same.
Sources and method
- FSANZ energy calculation notes — Official label energy factors and why simplified kcal arithmetic is approximate.
- FSANZ nutrition information panels — Using actual product values when turning targets into food.