Macro Calculator — Protein, Fat & Carbs

A calorie target on its own does not tell you what to put on the plate. Two diets at 2,400 kcal can hold 90 g of protein or 240 g, and for anyone training that difference is most of the point. The Macro Calculator turns one daily number into grams of protein, fat and carbs, then divides them across your meals.

There are two ways in. By body weight sets protein in grams per kilogram and fat as a share of calories, and carbs take what is left. That is how most sports-nutrition guidance is written. The Percentage split uses one of five presets, from Balanced 25/30/45 to Keto 20/75/5, or a custom split of your own.

Worked Example: 2,400 kcal at 80 kg

The page opens on 2400 kcal, 80 kg, protein at 2.0 g/kg, fat at 25% and four meals. The results:

• Protein: 160 g, which is 640 kcal or 26.7% of the day.
• Fat: 25% of 2,400 is 600 kcal, so 67 g after rounding (0.8 g/kg).
• Carbs: the remaining 1,160 kcal, exactly 290 g (48.3%).
• Each of the four meals: 40 g protein, 17 g fat, 73 g carbs.

Load Sample moves on to a balanced 2,000 kcal plan, then a keto plan entered in pounds, then a five-meal plan at 2,800 kcal.

How the Math Turns Calories into Grams

Grams come from the Atwater factors: 4 kcal per gram for protein and carbs, 9 for fat. In body-weight mode, protein is g/kg × weight × 4 and fat is calories × fat%. Carbs are whatever remains. If protein and fat together exceed the target, there is nothing left for carbs and the tool stops with a message saying how many kilocalories they already use.

Fibre is set at 14 g per 1,000 kcal, the US Dietary Guidelines figure, which gives about 34 g for the sample. Weight typed in pounds is divided by 2.20462 before any per-kilogram number is shown. The kg button next to the weight field converts the number you typed rather than just relabelling it.

Accuracy Limits of a Macro Split

Whole-gram rounding shifts the total slightly. The sample's grams add up to 2,403 kcal, three over the target, and the note under the table says so rather than hiding it. Protein outside 0.6–3.5 g/kg is refused with “Protein must be between 0.6 and 3.5 g per kg of body weight.”

Any macro outside the adult AMDR range (protein 10–35%, fat 20–35%, carbs 45–65%) is flagged. On the Keto preset, carbs at 5% are flagged as expected rather than as a mistake. Picking Custom starts from the preset already on screen, so small tweaks do not mean retyping three numbers. None of this replaces advice for kidney disease, diabetes or pregnancy, where protein and carb targets are set clinically.