Recipe Scaler (servings)

Understanding the recipe scaler — concept and principle

A recipe written for four people rarely matches the number you are cooking for. Scaling multiplies every ingredient by the same factor so the proportions, and therefore the taste and texture, stay the same. This calculator finds the scale factor from the original and new servings and applies it to a list of ingredient amounts in one go.

How it is calculated

• Scale factor k = new servings ÷ original servings.
• Scaled amount = original amount × k, for every ingredient.
• The results are rounded to 3 significant figures, which is more precise than any kitchen scale or measuring spoon needs.

Units do not change: grams stay grams, cups stay cups, and a count of eggs stays a count. Enter the numbers only, separated by commas or one per line, and keep track of the units yourself.

The principle

A recipe is a set of ratios. If 500 g of flour feeds four, then each serving uses 125 g, and six servings need 6 × 125 = 750 g. Dividing by the original servings and multiplying by the new ones is the same as multiplying by k. Because every ingredient is multiplied by the same number, all the ratios between ingredients (flour to liquid, salt to meat, sugar to butter) are preserved. This is why weighing in grams makes scaling easy and accurate.

Worked example

1. Inputs: original 4 servings, new 6 servings, amounts 500, 2, 250, 1.5.
2. Scale factor: 6 ÷ 4 = 1.5.
3. 500 × 1.5 = 750; 2 × 1.5 = 3; 250 × 1.5 = 375; 1.5 × 1.5 = 2.25.
4. Scaled amounts: 750, 3, 375, 2.25.

How to read the result

Ingredients scale cleanly, but cooking does not always. A larger pot takes longer to come to the boil, and a bigger roast needs more time; a thin sheet of biscuits bakes in about the same time whatever the quantity. In baking, choosing the right pan size usually matters more than the timer: keep the batter depth similar and the time will change little. Seasonings, strong spices and leavening are best scaled and then adjusted to taste or checked, since evaporation and pan area change with size.

Common mistakes

• Rounding awkward amounts too far: 2.25 eggs can be two large eggs plus a little beaten egg, not simply two.
• Scaling cooking time by the same factor as the ingredients.
• Overfilling a pan or pot when scaling up.
• Mixing volume and weight measures in the same list.

Frequently asked questions

How do I halve a recipe?

Enter the new servings as half of the original; the factor becomes 0.5 and every amount is halved.

How do I scale eggs?

Weigh them: a beaten egg can be divided by weight, so fractional eggs are possible.

Can I scale by ingredient instead of servings?

Yes. If you only have 300 g of an ingredient that the recipe uses 500 g of, the factor is 300 ÷ 500 = 0.6; enter servings in that ratio.

Sources: Harold McGee — On Food and Cooking: The Science and Lore of the Kitchen (Scribner, 2004)