Going from 4 to 6 servings makes every ingredient grow in the same proportion. The factor comes from a single division, and then it is applied to each line of the list. For more everyday cases, see fractions in everyday life.
Worked example: a dough from 4 to 6 servings
The recipe for 4 servings calls for `flour; 3/4; cup`, `salt; 1/2; teaspoon` and `eggs; 2; whole`. What amounts do you need for 6?
- Find the factor. 6 ÷ 4 = 3/2.
- Multiply the flour. (3/4) × (3/2) = 9/8, which is 1 1/8 cups.
- Multiply the salt. (1/2) × (3/2) = 3/4 teaspoon.
- Multiply the eggs. 2 × 3/2 = 3 eggs.
Result: 1 1/8 cups of flour, 3/4 teaspoon of salt and 3 eggs.
Check: 0.75 × 1.5 = 1.125, which is 9/8.
To shrink a recipe the factor is below 1: if you start from the amounts for 6 servings (3/4 cup of flour), going from 6 to 4 the factor is 2/3 and the flour drops to 1/2 cup. The table below collects more changes, with scale-ups and one reduction.
How the amounts change with other factors
The table starts from the amounts in the example and takes them to other numbers of servings. Factors with denominator 2 or 4 give amounts that are easy to measure with cups and spoons. The amounts are fractions, not rounded.
| Ingredient (starting amount) | 4 to 5, factor 5/4 | 4 to 10, factor 5/2 | 6 to 4, factor 2/3 (starting from the amounts for 6) |
|---|---|---|---|
| Flour, 3/4 cup | 15/16 | 15/8 = 1 7/8 | 1/2 |
| Salt, 1/2 teaspoon | 5/8 | 5/4 = 1 1/4 | 1/3 |
| Eggs, 2 | 5/2 | 5 | 4/3 = 1 1/3 |
Why you multiply instead of adding
A recipe is a proportion: for each ingredient, the new amount and the original keep the same ratio. In math this is called direct proportionality, and English Wikipedia describes it as a relation y = kx with a constant k; here k is the factor. Adding the same amount to everything breaks that relation, because one more cup is a lot for a small ingredient and very little for a large one.
What does not scale linearly
The multiplication is exact for the amounts, but cooking is not always. Salt, spices, yeast and baking time do not adjust the same way when you double or cut a recipe a lot, so use the result as a starting point and correct to taste or by the recipe. The calculator also does not convert volume to weight: it does not know how much a cup of each ingredient weighs, and a cup is not the same everywhere (a US cup is about 237 ml, a metric cup 250 ml), so weigh when accuracy matters.
What to enter in each field
- Enter the original and new servings, for example
4and6. Decimals such as2.5work. - Add one ingredient per line in the format
name; amount; unit. - Select “Calculate” to see the factor and the list, and “Print result” if you want it on paper.
If you prefer the result as a mixed number, the page on improper fraction to mixed number does the conversion, and the work by hand is explained in multiplying fractions.
Other tools for amounts and proportions
If you only need part of an amount, such as 2/5 of 200 g, use fraction of a number. To find an unknown, for example how many servings 500 g of flour makes, set up a rule of three or a proportion. When a total has to be split among parts of different weight, proportional sharing solves it. More everyday cases, from hours to measurements, are in the applications index.
Source: English Wikipedia, article Proportionality (mathematics), section “Direct proportionality”, which defines the relation y = kx with a positive constant k (accessed October 17, 2026).
Frequently asked questions
What do I do when the result is 2 1/4 eggs?
With one egg in the recipe for 4 servings, scaling it to 9 calls for 9/4 of an egg, which is 2 1/4. You cannot crack a quarter of an egg, so beat two eggs, split the beaten egg in half by weight and use 2 1/4 times that half. If the mixture allows it, you can also round to two.
How do I measure a third with spoons?
A factor with denominator 3 leaves thirds, which no spoon measures directly. If one tablespoon becomes 7/3, that is 2 1/3 tablespoons, and since a tablespoon holds 3 teaspoons, the third is 1 teaspoon: 2 tablespoons and 1 teaspoon. For thirds of other measures, weigh the ingredient.
What if I also change the pan?
Scale by the area of the bottom, not only by the servings. In a round pan, going from a 20 cm to a 26 cm diameter (about 8 to 10 inches) multiplies the area by 13/10 × 13/10 = 169/100, almost 1.7 times, because the diameter is squared. Use that number as the factor and keep the depth of the batter.
Can I scale to match what I have at home?
Yes. If the recipe calls for 250 g of an ingredient and you only want to use the 450 g you have, the factor is 450 ÷ 250 = 9/5. Enter 450 as the new servings and 250 as the original, and the calculator multiplies the rest: 150 g of sugar becomes 150 × 9/5 = 270 g.