How to Calculate Your Macros and Daily Calorie Needs
The math behind macro splits, calorie targets, and the Atwater factors that turn grams into calories.
Nutrition tracking apps make macro math look complicated, but it's really just a calorie budget split three ways, using a fixed conversion rate for each macronutrient.
The Atwater factors: calories per gram
Protein and carbohydrates both provide about 4 kilocalories per gram; fat provides about 9 kilocalories per gram — more than twice as energy-dense. These "Atwater factors" are what nutrition labels use to calculate total calories from the grams of each macro listed, and they're also how macro calculators convert a percentage split into actual grams.
Turning a calorie target into grams
Say your daily target is 2,200 calories with a 30% protein / 40% carb / 30% fat split. Protein: (2,200 × 0.30) / 4 = 660/4 = 165g. Carbs: (2,200 × 0.40) / 4 = 880/4 = 220g. Fat: (2,200 × 0.30) / 9 = 660/9 ≈ 73.3g. Notice fat gets the smallest gram amount despite having the same percentage as protein — because each gram of fat "costs" more than double the calories.
Protein targets scale with body weight, not just calories
Unlike carbs and fat, protein recommendations are often given directly in grams per kilogram of body weight rather than as a percentage of calories — commonly 1.6–2.2 g/kg for people doing regular resistance training. A 75kg person targeting 1.8 g/kg needs 75 × 1.8 = 135g of protein per day, regardless of their total calorie target that day.
Calories burned during exercise
Exercise calorie burn is commonly estimated using MET (Metabolic Equivalent of Task) values, which express exercise intensity as a multiple of resting metabolism. The formula is Calories = MET × 3.5 × weight(kg) / 200 × minutes. Running (MET ≈ 9.8) for 30 minutes at 75kg burns roughly 9.8 × 3.5 × 75 / 200 × 30 ≈ 386 calories — higher-MET activities burn more per minute at the same body weight.
Putting a full day together
Your Total Daily Energy Expenditure (TDEE) — resting metabolism plus activity — sets your calorie ceiling for maintenance; eating below it creates a deficit for weight loss (roughly 3,850 kcal of weekly deficit per pound lost), above it creates a surplus for weight or muscle gain.
- The macro calculator turns any calorie target and split into grams
- The calorie calculator derives a target calorie number from your TDEE and a weight change goal
- The protein intake calculator and calories burned calculator cover the other two pieces above