Nutrition
As of 2026-04-24
How Macro Calculator works
Methodology for the Macro Calculator: formulas, coefficients, data sources, assumptions, and known limitations.
Scope
Converts a daily calorie target into grams of protein, carbohydrate, and fat based on a chosen macro split.
Formula
grams = calories * macro_share / kcal_per_g, with kcal_per_g = 4 (P), 4 (C), 9 (F).
Coefficients
| Parameter | Value | Note |
|---|---|---|
| Protein energy | 4 kcal/g | |
| Carb energy | 4 kcal/g | |
| Fat energy | 9 kcal/g | |
| Alcohol energy (not modeled) | 7 kcal/g |
Data sources
- Atwater general factors (USDA). — 4-4-9 kcal-per-gram factors for protein, carbohydrate, and fat.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC: The National Academies Press, 2005. — Source for the AMDR ranges (10–35% P, 45–65% C, 20–35% F) used as defaults.
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. — PMID 28642676. Primary academic basis for the 1.4–2.0 g/kg/day protein guidance offered in higher-protein splits.
Assumptions
- Daily calorie target is accurate (usually from the TDEE calculator).
- Alcohol is not consumed or is ignored.
Approximation range
Arithmetic is exact given inputs. The real uncertainty lives in the calorie target upstream and in the chosen macro split.
Limitations
- Does not model fiber, micronutrients, or meal timing.
- Chosen split is user preference; the tool does not argue for one split over another.
Reproducibility
2500 kcal, 30/40/30 split. Protein = 2500*0.30/4 = 188 g. Carbs = 250 g. Fat = 83 g.
Change log
- 2026-04-24: methodology page first published.
Related tools
- TDEE Calculator — Estimate your daily energy expenditure with Mifflin-St Jeor + activity factors.
- BMR Calculator — Estimate basal metabolic rate and maintenance calories using Mifflin-St Jeor assumptions.
- Protein Intake Calculator — Get daily protein targets based on training level and goal.
- Water Intake Calculator — Calculate daily water intake based on weight, activity level, and climate.