Which formula is used here?

Uses goal-adjusted calorie targets, bodyweight-based protein ranges, and selected carb/fat split assumptions.

Can I use metric or imperial units?

Yes. This tool supports both metric and imperial units and remembers your preference.

Is this medical advice?

No. This tool provides general fitness estimates and should not replace medical guidance.

Is this tool free and private to use?

Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.

Do these tools replace medical guidance?

No. These outputs are general fitness estimates — not medical advice.

Can I switch between metric and imperial units?

Yes. Every tool supports both systems and remembers your preference in localStorage.

Methodology: Macro Calculator

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.

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.

Worked example

Computed by the same engine bundle served at /engines/macro-calculator.js. Re-runnable: the values below are the literal output of compute(engineInput).

Input

tool: macro_calculator
calories: 2200
weight_kg: 80

Output

targetCalories: 2200
proteinGrams: 144
carbGrams: 203
fatGrams: 90.222222

FAQ

Which formula is used here?: Uses goal-adjusted calorie targets, bodyweight-based protein ranges, and selected carb/fat split assumptions.
Can I use metric or imperial units?: Yes. This tool supports both metric and imperial units and remembers your preference.
Is this medical advice?: No. This tool provides general fitness estimates and should not replace medical guidance.
Is this tool free and private to use?: Yes. AI Fit Hub tools are free, no-signup browser tools. Inputs stay in your browser unless you choose to share a URL.
Do these tools replace medical guidance?: No. These outputs are general fitness estimates — not medical advice.
Can I switch between metric and imperial units?: Yes. Every tool supports both systems and remembers your preference in localStorage.