What is the Atwater cross-check?

Protein and carbs each contribute 4 kcal/g; fat contributes 9 kcal/g (the Atwater factors). Multiplied out and summed, the total should match the kcal figure within ~5%. Bigger gaps mean a data-entry error.

How many portions to plan for?

Common: 4-6 portions for weekday lunch meal prep. Lower portion count = more food per meal; higher = smaller portions to last longer.

Should I include water weight?

No — water has 0 kcal but it changes the portion-size feel. Weigh portions by total cooked weight for consistency.

What if my meal-prep needs vary by day?

Set the target to the average; mix and match portions through the week. Days with extra workouts may take a higher-calorie portion than rest days.

What is the Atwater cross-check?

Protein and carbs each contribute 4 kcal/g; fat contributes 9 kcal/g (the Atwater factors). Multiplied out and summed, the total should match the kcal figure within ~5%. Bigger gaps mean a data-entry error.

How many portions to plan for?

Common: 4-6 portions for weekday lunch meal prep. Lower portion count = more food per meal; higher = smaller portions to last longer.

Should I include water weight?

No — water has 0 kcal but it changes the portion-size feel. Weigh portions by total cooked weight for consistency.

What if my meal-prep needs vary by day?

Set the target to the average; mix and match portions through the week. Days with extra workouts may take a higher-calorie portion than rest days.

Meal-Prep Calorie Calculator

Total recipe kcal + macros + number of portions → per-portion kcal and macros, with daily-target check.

Result

Per portion

480 kcal

P 36.0 · C 60.0 · F 12.0 · On target

Recipe totalsP 180.0g · C 300.0g · F 60.0g2,400 kcal
Atwater cross-checkMacros consistent with kcal2,460 kcal from macros
Portions5
Per-portion kcal480
Per-portion P/C/F36.0 / 60.0 / 12.0 g
Per-portion macro %P 30% · C 50% · F 23%
Target per meal500 kcal
Delta from targetOn target

Step-by-step

Per-portion = total / portions; identical for kcal, P, C, F.
Atwater cross-check: P×4 + C×4 + F×9 = 2,460 kcal vs stated 2,400 kcal.

How to use this calculator

Enter the recipe totals (kcal + protein/carb/fat grams) — typically from a nutrition app or our recipe-nutrition calculator.
Enter the number of portions you'll split it into.
Enter your target per-meal calorie figure.
Read per-portion macros and the variance from target.

About this calculator

Meal-prep math is one division: total kcal ÷ portions = per-portion kcal. The Atwater cross-check (P×4 + C×4 + F×9 vs stated kcal) catches data-entry errors — if the two disagree by more than 5%, something is wrong with the macro entry. The daily-target delta tells you whether your prep matches your eating plan: 5% slack is normal, 10%+ should prompt a recipe adjustment.

What this calculator does

This calculator takes total recipe calories and macro grams (protein/carb/fat), divides by the number of portions to produce per-portion values, runs an Atwater cross-check to flag macro/kcal mismatches, and compares per-portion kcal against a daily-target figure. The output is a single coherent per-portion macro card plus a "this matches your plan" or "X kcal over/under" verdict.

How it works — the formula

per_portion_X = total_X / portions  (for X in kcal, P, C, F)
Atwater check: total_kcal ≈ 4·P + 4·C + 9·F
delta_from_target = per_portion_kcal − target_kcal_per_meal

Straight division and one bookkeeping cross-check. The Atwater identity (4/4/9 kcal/g for P/C/F) is the same convention used on every FDA Nutrition Facts label and is the simplest available check for internal consistency. A >5% gap usually means a typo in one of the macro entries.

Sources: FDA Nutrition Facts Label — 21 CFR 101.9 (Atwater factors) · USDA FoodData Central · Atwater W.O. — Atwater factor methodology (1900, foundational for modern nutrition labeling)

Worked examples

Example 1

High-protein weekly prep

Inputs:: 2400 kcal / 180P / 300C / 60F / 5 portions / 500 kcal target
Output:: Per-portion 480 kcal; P 36 · C 60 · F 12; on-target (within 5%)

Standard 5-portion lunch prep within the daily target.

Example 2

Calorie-over alert

Inputs:: 3000 kcal / 200P / 350C / 90F / 4 portions / 500 kcal
Output:: Per-portion 750 kcal; 250 kcal over target

Either split into more portions or reduce the recipe.

Example 3

Atwater mismatch flag

Inputs:: 1000 kcal / 30P / 100C / 50F (= 970 by Atwater)
Output:: Mismatch ~3% — within tolerance

Sub-5% mismatches are normal; >10% suggests a typo.

When to use this vs other tools

Use this for portioning a known recipe. To compute the recipe totals first, use the recipe-nutrition tool below.

Recipe Nutrition Facts
Use to compute the recipe totals (kcal + macros) that feed into this calculator.
Smoothie Nutrition
Use for liquid-meal nutrition with a curated smoothie-ingredient list.
Macros per Serving
Use to set the per-meal macro target (the input to this calculator).
Macro-Friendly Recipe Scaler
Use to scale a recipe up or down while preserving the P/C/F ratio.

Authority note

USDA FoodData Central + FDA

FDA 21 CFR 101.9 Nutrition Facts labeling rules — codifies the Atwater 4/4/9 factor convention used here

FDA 21 CFR 101.9 is the binding US regulation for Nutrition Facts labels and the Atwater factor convention used here. Recipe totals should come from USDA FDC values.

Limitations

Assumes equal-size portions. Real meal prep often varies (lunch larger than dinner); compute each portion size separately if needed.
Atwater 4/4/9 is an approximation; true metabolizable energy can deviate by a few % for fiber-rich, fat-rich, or alcohol-containing foods.
No micronutrient tracking (vitamins, minerals, sodium).
Total kcal target is per-meal; for daily totals multiply by meals/day.

For medical or sport-nutrition planning consult a registered dietitian. This tool is for everyday meal-prep portioning.

Frequently asked

Use the recipe-nutrition calculator on this site, or any food tracker (MyFitnessPal, Cronometer). The Atwater cross-check below will tell you if the numbers are internally consistent.