How to scale a recipe without ruining it

Scaling a recipe gives you new ingredient quantities. It leaves a few practical questions: how to measure part of an egg, which tin to use, and when to check the food. Work those out before you start, rather than discovering them halfway through mixing.

The factor itself

Divide the servings you want by the servings the recipe makes:

factor = desired servings ÷ original servings

6 people from a 4-person recipe  →  6 ÷ 4 = 1.5

The recipe scaler applies this factor to the quantity at the start of each ingredient line. With Kitchen fractions (3/4) selected, these illustrative lines produce:

Original line	At ×1.5
200 g plain flour	300 g plain flour
3/4 cup milk	1 1/8 cup milk
1½ tbsp olive oil	2 1/4 tbsp olive oil
2–3 cloves garlic	3–4 1/2 cloves garlic
3 large eggs	4 1/2 large eggs
salt to taste	salt to taste

These are quantity examples, not a tested recipe. Five of the six lines scale; the last has no number to change.

Make the ingredient list unambiguous

Put one ingredient on each line, with its quantity first. Remove bullets and list numbers. - 200 g flour is not recognised as a leading quantity; 1. 200 g flour starts with a list number that can be mistaken for one.

The tool handles ingredient fractions such as 1 1/2, ½ and 2½, as well as ranges and prefixes such as about. The serving boxes and the multiplier control are different: use a decimal such as 0.5 there, not 1/2.

Only the leading quantity changes. This helps with packs: 2 × 400 g tins of tomatoes becomes 3 × 400 g tins of tomatoes at ×1.5. It needs care with alternative measurements: 200 g flour (about 1 1/2 cups) becomes 300 g flour (about 1 1/2 cups). The bracketed cup amount is now wrong; remove or correct it in the copy you cook from.

Fractions, rounding and units

Three quarters multiplied by 1.5 is exactly 1.125. Fraction mode displays 1 1/8; decimal mode rounds it to 1.13. Fraction mode uses halves, thirds, quarters, sixths and eighths when a close match is available, with a decimal fallback. It is a display choice, not a guarantee of exact measurement. Very small results can round to zero.

Units stay as entered. There is no cups-to-grams conversion, and 1500 g does not become 1.5 kg. Where the original recipe supplies weights, using those avoids awkward cup and spoon divisions. King Arthur Baking’s guide to reducing a recipe recommends weighing ingredients for this reason.

Handle partial eggs and review the flags

For a whole egg that will be mixed into the batter, whisk the yolk and white together and weigh out the portion you need. For example, half of an egg weighing 56 g out of its shell is 28 g. That is a hypothetical weight, not a standard size for every egg. Measure yolks and whites separately when the recipe uses them separately. The King Arthur guide above explains this weighing method.

The scaler’s Needs a decision notes come from word matching. Eggs, yeast, baking powder, salt and several other terms trigger them; even garlic can be flagged through the word “cloves”. The tool still applies the same factor and does not decide how much of an ingredient to hold back.

Keep the tested recipe’s proportions as your starting point. A flag is not a reason to apply a blanket reduction to salt, yeast or raising agents. King Arthur’s baker’s percentage reference shows bread formulae being scaled while retaining ingredient ratios, including salt and yeast. Changes to the method or proving conditions need recipe-specific judgement.

Match the tin to the quantity

Doubling a cake recipe made in one 20 cm round tin is straightforward to portion into two matching 20 cm tins. Putting all of that batter in the original tin makes it deeper and may leave too little room for rising.

If you want one larger cake, a 28 cm round tin gives roughly the same batter depth for a double batch. A 25 cm round is smaller than that, so it is not a like-for-like replacement. Check the usable depth as well as the width, and follow any fill guidance in the recipe.

Use the baking pan converter when your available tin has a different shape or size. Its comparison helps you choose the quantity; it cannot tell whether the new shape will bake well. King Arthur’s pan-substitution guide explains these limits, including differences in material and shape.

Keep the timing decision separate

A factor of 1.5 does not turn a 40-minute bake into a 60-minute bake. The calculator does not know your oven, equipment or batter depth. Use the original recipe’s doneness cues and check early after changing the batch or tin; do not multiply its time or temperature by the ingredient factor. King Arthur’s reducing guide explicitly notes that there is no fixed calculation for the new baking time.

Before cooking, save the scaled list, check its unchanged notes, decide how to measure fractional ingredients and choose the equipment. That leaves you with a usable recipe rather than just a column of new numbers.

Last reviewed 2 October 2026.