Recipe Scaling Calculator

Intro

Use this recipe scaling calculator to halve a recipe, double an ingredient list or change its number of servings. Enter fractions or decimals and see each scaled amount in the original units. Notes such as “Salt to taste” stay unchanged and are explicitly marked as not scaled.

What this calculator does

Choose Change servings, Half the recipe, Double the recipe or a Custom factor. Enter one ingredient per line, starting with an amount and a space: `1 1/2 cups flour`, `200 g flour` or `1 (14-ounce) can tomatoes`. Ingredient names, package sizes and unit labels remain as written; duplicate lines stay separate.

Whole numbers, decimals with a period, simple fractions, mixed numbers and common Unicode fractions such as ½ are accepted. Write `1 1/2`, rather than `1 and 1/2`. Remove bullets, signs and ranges such as `1–2 cups`; choose one definite quantity. A line without a numeric amount is retained, but a list needs at least one quantified ingredient.

How it works

The servings method follows the proportional recipe-adjustment method in the Institute of Child Nutrition's Adjusting Standardized Recipes material, slide 10:

`Scaling factor = target servings / original servings`

`Scaled ingredient amount = original ingredient amount × scaling factor`

For half a recipe the factor is 1/2; doubling uses 2. Custom mode accepts an exact fraction or decimal factor from 1/1000 through 1000. Every calculation starts from your original ingredient amounts. Resubmitting or changing the display cannot compound rounding.

Select Scale recipe to calculate. Editing any input clears the earlier amounts until you calculate again. Reset restores the sample list. This browser tool requires JavaScript and native BigInt support to preserve exact arithmetic.

Example calculation

The sample list illustrates quantity arithmetic; it is not a tested recipe. For 4 original servings and 2 target servings, the factor is 2/4 = 1/2:

• 1 1/2 cups flour → 3/4 cups flour.
• 3/4 cup sugar → 3/8 cup sugar.
• 2 large eggs → 1 large eggs.
• 0.5 tsp salt → 1/4 tsp salt.
• Salt to taste → Salt to taste — kept as written, not scaled.

The original labels are preserved, including singular/plural wording. For 4 original servings and 6 target servings, the factor is 6/4 = 1 1/2:

• 1 1/2 cups flour → 2 1/4 cups flour.
• 3/4 cup sugar → 1 1/8 cup sugar.
• 2 large eggs → 3 large eggs.
• 0.5 tsp salt → 3/4 tsp salt.
• Salt to taste → Salt to taste — kept as written, not scaled.

As a separate rounding example, 0.1 units multiplied by 1/3 is exactly 1/30. At four decimal places it displays 0.0333, with the exact fraction alongside. A half-up tie such as 1.005 at two places displays 1.01.

How to use the result

Check each original line against its scaled amount. Fraction mode shows reduced exact mixed fractions. Decimal mode rounds half up to two, three or four decimal places and retains the exact fraction in the table. Trailing zeros are omitted.

A tiny positive amount that rounds to zero displays a threshold such as <0.001, with its exact value alongside; a true zero remains 0. Three eggs halved are 1 1/2 eggs. The tool does not round whole items or tell you how to prepare a fractional egg. Check how to measure the amount in your own recipe.

Saving is optional and uses the existing local Save control. A shared link includes your entered ingredients in its fragment and is readable by anyone who receives it. Avoid sharing private recipes unintentionally. Printing is user initiated; no ingredient list is uploaded by this calculator.

Assumptions and limitations

Only ingredient quantities are scaled. Cooking time, oven temperature, pan size, mixing technique, nutrition and food safety are not calculated. Large changes can require recipe testing; equal proportions alone do not guarantee the same cooking outcome. “Servings” is your batch count, not a nutritional serving-size definition.

Units stay exactly as entered. US and UK cups, tablespoons and ounces are not reinterpreted, and cups are not converted to grams. Density depends on the ingredient and its measurement method. Use the separate Volume Converter for supported volume-unit conversions, checking its unit definitions.

Input limits are 3,000 characters overall, 20 nonblank lines and 140 characters per line, including at most 120 for its ingredient label. Amounts are at most 1,000,000; servings must be positive and at most 10,000. Numeric entries are at most 32 characters, with at most six decimal places. Fraction components are at most 1,000,000 with a positive denominator. The final scaling factor must be from 1/1000 to 1000. These are input limits, not recommended batch sizes. Invalid lines reject the complete calculation rather than showing a partly scaled recipe.

How we explain formulas, assumptions and sources