Macros are the three nutrients that supply energy: protein, carbohydrate, and fat. Calories determine whether your weight moves; the split between these three shapes how much of that change is muscle versus fat, and how easy the diet is to stick to.
- What it gives you
- Daily grams of protein, carbs, and fat
- Energy per gram
- Protein 4 · Carbs 4 · Fat 9
- Protein for muscle
- 1.6–2.2 g per kg body weight
- Minimum fat
- About 0.5 g per kg for hormone function
- Acceptable ranges
- IOM: 10–35% protein, 45–65% carbs, 20–35% fat
Formula
Percentage-of-calories split with Atwater energy factorsProtein (g) = calories × protein% ÷ 4 Carbohydrate (g) = calories × carb% ÷ 4 Fat (g) = calories × fat% ÷ 9
- calories
- — Your daily calorie target
- 4 and 9
- — Calories per gram — protein and carbohydrate 4, fat 9
Fat provides more than twice the energy per gram, which is why a high-fat split yields far fewer grams than the percentage suggests.
Macro Calculator examples
| Input | Result | Category |
|---|---|---|
| Man, 180 lb, maintain, balanced | 2,763 cal/day | Balanced · 30/40/30 |
| Man, 180 lb, cut, high protein | 2,263 cal/day | High protein · 40/35/25 |
| Man, 160 lb, bulk, balanced | 3,267 cal/day | Balanced · 30/40/30 |
| Woman, 150 lb, maintain, balanced | 2,172 cal/day | Balanced · 30/40/30 |
| Woman, 150 lb, cut, high protein | 1,672 cal/day | High protein · 40/35/25 |
| Woman, 140 lb, keto | 1,308 cal/day | Ketogenic · 25/5/70 |
How much protein do I need?
Protein is the macro worth setting first, because it has the clearest evidence base and the biggest effect on body composition.
| Situation | Grams per kg | Grams per lb |
|---|---|---|
| Sedentary adult (RDA minimum) | 0.8 | 0.36 |
| General health and activity | 1.2–1.6 | 0.55–0.73 |
| Building muscle | 1.6–2.2 | 0.73–1.0 |
| Losing weight while training | 1.6–2.4 | 0.73–1.1 |
| Adults over 65 | 1.0–1.2 | 0.45–0.55 |
The RDA of 0.8 g/kg is the amount that prevents deficiency, not the amount that optimises body composition. Intakes above roughly 2.2 g/kg show no further benefit for muscle in the research, so there is little point going higher.
Choosing a split
- Balanced (30/40/30) — the default. Suits most goals and is the easiest to eat normally.
- High protein (40/35/25) — best when losing weight, because it preserves the most lean mass and is the most filling per calorie.
- Low carb (35/20/45) — reduces carbohydrate without ketosis. Useful for appetite control and blood-sugar management.
- Ketogenic (25/5/70) — restricts carbohydrate far enough to shift the body to running on ketones, typically under 50 g a day.
- High carb (25/55/20) — supports glycogen for endurance training and high training volumes.
For weight change specifically, the split matters much less than the calorie total. Trials comparing low-carb with low-fat at matched calories and protein consistently find similar results. Choose the split you can actually follow.
Floors worth respecting
Two of the three macros have genuine minimums.
- Fat should not fall below about 0.5 g per kg of body weight. Fat is required to absorb vitamins A, D, E, and K and to produce sex hormones; very low intakes disrupt both.
- Carbohydrate has no strict dietary requirement — the body can make glucose from other sources — but very low intakes impair high-intensity performance and, for some people, sleep and mood.
- Protein has the highest practical minimum, since it is the only macro whose shortfall directly costs you muscle.
Do I have to hit my macros exactly?
No. Landing within about 5–10 g of each target is more than close enough, and food labels themselves carry a legal tolerance of roughly 20%.
Protein is the one worth being consistent about, since falling short repeatedly does have a measurable effect on lean mass in a deficit. Carbohydrate and fat can trade against each other freely as long as the calorie total holds.
Frequently asked questions
What is the best macro split for weight loss?
Higher protein splits, around 30–40% of calories, tend to work best. They preserve more lean mass in a deficit and are more filling per calorie. The carbohydrate-to-fat ratio matters far less — pick whichever you find easier to sustain.
How many grams of protein should I eat per day?
Between 1.6 and 2.2 grams per kilogram of body weight if you are training, which is roughly 0.7 to 1.0 grams per pound. Sedentary adults need at least 0.8 g/kg to avoid deficiency, but that is a floor rather than a target.
Do macros matter more than calories?
No. Calories determine whether weight goes up or down; macros shape the composition of that change and how easy the diet is to follow. Both matter, but calorie total is the primary lever.
What macros should I use for keto?
Roughly 5% of calories from carbohydrate, 25% from protein, and 70% from fat — usually under 50 grams of carbohydrate a day, and often under 20 to enter ketosis quickly.
Why are my fat grams so much lower than my carb grams?
Fat supplies 9 calories per gram against 4 for carbohydrate and protein. The same share of calories therefore buys you less than half as many grams of fat.
Should I track net carbs or total carbs?
Total carbohydrate is what this calculator gives you. Net carbs subtract fibre and sugar alcohols, which is common on ketogenic diets but is not a regulated term and varies by how it is calculated.
Sources
- Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids — Institute of Medicine, National Academies Press, 2005
- A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength — Morton et al., British Journal of Sports Medicine, 2018
- International Society of Sports Nutrition Position Stand: protein and exercise — Jäger et al., Journal of the International Society of Sports Nutrition, 2017
- Dietary Guidelines for Americans, 2020–2025 — US Departments of Agriculture and Health and Human Services, 2020