Macro Calculator

Protein, carbohydrate and fat are the three macronutrients that supply the body with usable energy, alongside alcohol, which supplies energy but is not considered a nutrient. The standard energy values used on food labels and in this calculator — 4 kcal per gram for protein and carbohydrate, 9 for fat — are known as the Atwater general factors, after the American chemist Wilbur Atwater, who established them through direct calorimetry experiments at the end of the 19th century. They remain the near-universal basis for food energy labelling worldwide, more than a century later.

Of the three macronutrients, protein has the highest thermic effect — the body spends more energy digesting and processing it than it does for carbohydrate or fat — and it is consistently found to be the most satiating per calorie, which is part of why it is typically set first when building a macro target and the other two are filled in around it. Protein also supplies the amino acids needed to preserve or build muscle tissue, a role carbohydrate and fat cannot substitute for regardless of how many calories they provide.

There is no single “correct” ratio of carbohydrate to fat — controlled research consistently finds that, once calories and protein are matched, different splits produce broadly similar results for fat loss. The splits offered here reflect common dietary patterns rather than a claim that any one is superior.

Tracking macronutrients rather than only total calories is most associated with bodybuilding and physique sport, where the “if it fits your macros” (IIFYM) approach to flexible dieting grew directly out of the sport’s longstanding emphasis on precise nutrition. It has since spread more broadly into general fitness tracking, though for most people outside competitive or physique-focused training, hitting a reasonable protein target and a sensible total calorie level matters far more than precisely matching a carbohydrate-to-fat ratio.