Recipe Scaler

How to scale a recipe

1. Choose By servings and enter original and target servings, or choose Direct multiplier.
2. Add named ingredients with an optional quantity and unit. Use the labelled up/down and remove buttons to edit the order; structural changes and Clear / Reset offer one-step Undo.
3. Choose decimal or exact fraction / mixed-number display. Review original and scaled amounts alongside the exact factor. Blank quantities stay unspecified; numeric zero remains zero.
4. Copy the complete recipe, download scaled-recipe.txt, or print the clean summary. Notes are included unchanged. Invalid fields block all final exports without discarding your entries.

Worked example: four servings to six

The factor is 6 / 4 = 3 / 2. An ingredient with 200 g becomes 300 g, and 1/2 tsp becomes 3/4 tsp (0.75 in decimal display). Salt to taste with no numeric quantity stays unspecified. One egg becomes 1 1/2 piece; the scaler does not silently round it to a whole item.

Supported quantities and fractions

Enter a nonnegative integer, a dot/comma decimal with up to four places, a fraction such as 1/2, or a proper mixed fraction such as 1 1/2. The common Unicode fractions ¼, ½ and ¾ work on their own or after an integer, with optional whitespace: 1½ and 1 ½ both mean 1 1/2.

Fraction numerators must be unsigned integers no greater than 1,000,000; denominators must be unsigned integers from 1 to 1000. Mixed fractions require a fractional part below one: 1 3/2 is rejected. Negative amounts, ranges, exponent notation, grouping separators, denominator zero and descriptive numeric text are not supported. Leave Quantity blank and put descriptive amounts in the ingredient name or notes.

A comma is a decimal separator, not grouping: 1,5 means 1.5, and 1,000 means 1.000. Servings permit at most two decimal places in the inclusive range 0.01–1000; direct multipliers permit four places in 0.0001–1000. Serving ratios can exceed the direct-multiplier range, but every entered and scaled quantity is capped at 1,000,000.

Exact arithmetic and display rounding

Reduced BigInt fractions retain exact values internally. Scaling always uses the original ingredient model, so changing the factor or display mode never compounds previous rounding. For example, 1/3 multiplied by 3 is exactly 1.

Default decimal display rounds half-up to at most three places and omits trailing zeros. Rounded amounts carry an approximation marker and their exact fraction. A positive amount that would round to zero instead says less than 0.001, with its exact value alongside. Fraction display uses reduced fractions and mixed numbers, or an integer without a denominator. Blank quantities are distinct from zero.

Units, notes and practical limitations

g, kg, mg, ml, l, tsp, tbsp, cup, oz, lb and piece are labels, as is custom text. Selecting kg after g does not rescale the amount. There is no regional cup assumption, teaspoon-to-millilitre conversion or ingredient-density calculation. Custom units can be blank if no label is needed.

Notes are plain text and copied unchanged. Cooking temperature/time and pan size are not adjusted automatically. Fractional counts are mathematical results, not instructions for practical preparation. This tool provides recipe arithmetic, not nutrition advice, cooking-safety guidance or automatic cooking-time prediction.

Limits: 100 ingredients, 200 characters per ingredient name, 30 per custom unit and 5000 for notes (browser UTF-16 character counts). Invalid entries are highlighted and preserved until you correct or remove them. This small bounded calculation runs synchronously; it needs no worker or remote service. Copy, UTF-8 download and clean print use the same complete summary, including factor, serving assumptions, display precision, ingredients and notes. Clipboard denial leaves the selectable summary available.

No URL scraping, OCR, AI parsing, accounts or image/workbook import. Inputs are not logged, persisted or put into links. Download URLs are released when invalidated or when leaving the tool; obsolete clipboard replies cannot override an edited recipe.