Scaling a recipe:
multiply by new ÷ old servings

How to scale a recipe

To scale a recipe, multiply every ingredient by the target servings divided by the original servings. A recipe for 4 that uses 250 g of flour needs 250 × 10 ÷ 4 = 625 g for 10 servings.

The Calcylator tool takes original servings and target servings (steppers from 1 to 100) and one ingredient quantity, and shows the scaled quantity to up to three decimals. Run it once per ingredient.

The scaling factor and a quick chart

Divide target by original once to get the scaling factor, then multiply every ingredient by it. Going from 4 to 6 servings gives 1.5, so 3 eggs become 4.5 and 100 g of butter becomes 150 g.

If you do many ingredients, writing the factor at the top of the recipe saves repeated division. A factor of 2 is simply doubling, and 0.5 is halving.

Awkward amounts: eggs, spoons and fractions

Scaling often produces amounts you cannot measure, such as 4.5 eggs or 0.75 of a teaspoon. Handle them in a sensible way instead of rounding blindly.

• Eggs: beat an egg in a cup, weigh it, and use the share you need. For 4.5 eggs, use 4 whole eggs and half of a fifth, beaten and divided.
• Small spoon amounts: three quarters of a teaspoon is a half plus a quarter, or move to a pinch.
• Grams are easier to scale than cups. If a recipe is in cups, convert it to grams first when you can.

A second worked example: a soup for 6 uses 900 ml of stock and you cook for 4. The factor is 4 ÷ 6 = 0.667, so the stock becomes 900 × 4 ÷ 6 = 600 ml.

What does not scale in a straight line

The maths scales amounts, but the cooking itself may not follow the same line. A bigger batch needs a bigger pan or pot, and the surface area of a pan grows with its size.

As an example, a recipe for 4 baked in a 20 cm square tin (400 cm²) scaled to 6 servings needs about 1.5 times the area, which is 600 cm², close to a 20 by 30 cm tin. Keep the depth similar and the baking time stays near the original, but check as it cooks.

Salt, strong spices, chilli and raising agents are usually safest to build up gradually: scale them, then taste and add more near the end rather than assuming the same factor is perfect.

Common mistakes when scaling a recipe

• Scaling most ingredients but forgetting one, such as the oil or the spices.
• Mixing units after scaling, for example grams for one ingredient and cups for another without a check.
• Keeping the same cooking time for a much larger or smaller batch.
• Using a pan that is too small, so the dish overflows or cooks unevenly.
• Entering the target and original servings the wrong way round, which inverts the result: halving instead of doubling.