Does this change the macro ratio?

No — that's the point. To change the ratio (e.g., add protein without more carbs), you must add or swap ingredients, not scale uniformly.

What does Atwater consistency check do?

Compares P×4 + C×4 + F×9 against the stated kcal. If they disagree by >10%, your input is likely a typo or comes from an unreliable source.

Can I scale up beyond 2x?

Math works for any positive scale factor, but practical recipes have non-scaling components (seasoning levels, cooking times, pan sizes). Scaling beyond 2-3× often needs cooking-method adjustments.

How do I change the ratio (not just the size)?

Add a single high-protein or high-fat ingredient to shift the ratio. Eyeball this calculator's scaled values, then nudge specific ingredients up or down to retarget.

Does this change the macro ratio?

No — that's the point. To change the ratio (e.g., add protein without more carbs), you must add or swap ingredients, not scale uniformly.

What does Atwater consistency check do?

Compares P×4 + C×4 + F×9 against the stated kcal. If they disagree by >10%, your input is likely a typo or comes from an unreliable source.

Can I scale up beyond 2x?

Math works for any positive scale factor, but practical recipes have non-scaling components (seasoning levels, cooking times, pan sizes). Scaling beyond 2-3× often needs cooking-method adjustments.

How do I change the ratio (not just the size)?

Add a single high-protein or high-fat ingredient to shift the ratio. Eyeball this calculator's scaled values, then nudge specific ingredients up or down to retarget.

Macro-Friendly Recipe Scaler

Scale a recipe to a target calorie count while preserving the protein/carb/fat ratio.

Result

Scale factor

×1.500

Target 1,800 kcal · ratio preserved

Original kcal1,200
Target kcal1,800
Scale factor1.5000
Original P/C/FP 27% · C 40% · F 30%80.0 / 120.0 / 40.0 g
Scaled P/C/FMultiply every ingredient by the scale factor120.0 / 180.0 / 60.0 g
Atwater consistencyOK (within 10%)

Step-by-step

Scale factor = target / current = 1,800 / 1,200 = 1.5000.
Multiply every ingredient (and therefore P, C, F) by 1.5000.
Ratios preserved: P/C/F % unchanged from original.

How to use this calculator

Enter the current recipe's kcal and macros (typically from recipe-nutrition).
Enter your target kcal.
Read the scale factor and the scaled macros. Multiply every ingredient amount by the scale factor.

About this calculator

A macro-friendly scaler preserves the protein/carb/fat ratio while changing the total calorie count. Because kcal = 4P + 4C + 9F (Atwater), multiplying every ingredient by the same scale factor multiplies kcal, P, C, and F all by that factor — keeping the ratio constant. This is the math behind "bulk this up 1.5×" or "cut this by 25%" in meal-plan adjustments.

What this calculator does

This calculator computes the scale factor needed to bring a recipe from its current calorie total to a target calorie total, and reports the scaled protein/carb/fat grams. The P/C/F ratio is preserved exactly because every ingredient (and therefore every macro) is multiplied by the same number. An Atwater-consistency flag catches input errors when stated macros don't match the stated kcal.

How it works — the formula

scale = target_kcal / current_kcal
new_P = current_P × scale
new_C = current_C × scale
new_F = current_F × scale
(P/C/F % unchanged: each percentage = (macro × Atwater_factor) / total_kcal, and both numerator and denominator scale by the same factor.)

Uniform scaling is the only operation that preserves both the calorie count and the macro ratio. To preserve only one, use a different transformation (e.g., add carbs to raise kcal without changing protein). The Atwater 4/4/9 convention is the FDA standard for nutrition labels and is the basis for the consistency check here.

Sources: FDA Nutrition Facts Label — 21 CFR 101.9 (Atwater factor convention) · USDA FoodData Central — for the per-ingredient values that feed into recipe totals · Atwater W.O. — Atwater factor methodology (1900, foundational)

Worked examples

Example 1

Scaling up for lean bulk

Inputs:: 1200 kcal → 1800 kcal (80P/120C/40F)
Output:: scale ×1.5; new 120P / 180C / 60F

Same recipe, 50% more of every ingredient.

Example 2

Cutting for fat loss

Inputs:: 1200 kcal → 900 kcal
Output:: scale ×0.75; new 60P / 90C / 30F

Same recipe, 75% of every ingredient — useful for a calorie deficit week.

Example 3

Atwater warning

Inputs:: 500 kcal / 100P / 100C / 100F (=1700 by Atwater)
Output:: Warning: macros and kcal disagree by >10%

Either the kcal or one of the macros is mis-entered.

When to use this vs other tools

Use this to scale recipe portions while keeping macro ratios constant. To change the ratio itself, you need to add or swap ingredients.

Recipe Nutrition Facts
Use to compute the input totals from individual ingredients.
Meal-Prep Calories
Use to divide the scaled total across portions and compare against a daily target.
Macros per Serving
Use to set a fresh per-serving macro target — the inverse direction.
Recipe Scaler
Use to scale by yield (servings) rather than by calorie target.

Authority note

FDA + USDA

FDA 21 CFR 101.9 Nutrition Facts labeling rules (Atwater factors) and USDA FoodData Central (per-ingredient values)

The Atwater 4/4/9 convention is the FDA standard for US nutrition labels and is the basis for every macro-vs-kcal consistency check. Recipe inputs should come from USDA FDC values for best accuracy.

Limitations

Uniform scaling preserves ratio but not flavor balance — seasoning, leavening, and herbs often don't scale linearly.
Practical cooking limits — doubling a recipe may need a bigger pan or different cooking time.
Doesn't change the macro ratio. For ratio changes, add/swap ingredients individually.
Atwater factor cross-check tolerance is 10%; smaller deviations are normal for fiber-rich or alcohol-containing foods.

Recipe scaling math is exact; cooking results depend on technique. Adjust seasoning and cook time when scaling beyond 2-3×.