What is scale factor?
A scale factor is the number you multiply by when increasing or decreasing a recipe, drawing, ratio or quantity.
A scale factor is a multiplier used to make something larger or smaller. In cooking, it tells you how much to multiply each ingredient by when changing the recipe yield or number of servings.
If the scale factor is greater than 1, the recipe is being increased. If it is less than 1, the recipe is being reduced. If it is exactly 1, the recipe stays the same size.
Scale factor formula
For recipes, the scale factor is usually worked out by dividing the desired number of servings by the original number of servings.
scale factor = desired servings ÷ original servingsOnce you know the scale factor, multiply each ingredient amount by that number.
new ingredient amount = original amount × scale factorScale factor examples
Here are common cooking examples showing how the scale factor changes a recipe.
| Original recipe | Desired recipe | Scale factor | What it means |
|---|---|---|---|
| Serves 4 | Serves 8 | 2 | Double every ingredient. |
| Serves 6 | Serves 3 | 0.5 | Halve every ingredient. |
| Serves 4 | Serves 10 | 2.5 | Multiply each amount by 2.5. |
| 12 muffins | 18 muffins | 1.5 | Increase ingredient amounts by half again. |
Ingredient example
Suppose a recipe serves 4 and uses 300g flour. You want the recipe to serve 10.
10 ÷ 4 = 2.5300g × 2.5 = 750g flourThe same multiplier can be used for the other ingredients, although some items may need kitchen judgement.
Scale ingredients automatically
Enter your original servings, desired servings and ingredients to calculate the scale factor and updated quantities.
Scale factor greater than 1, less than 1 or equal to 1
The size of the scale factor tells you what is happening to the recipe.
When scale factors need rounding
Scale factors often create awkward ingredient amounts, especially with teaspoons, tablespoons, eggs and small quantities of seasoning.
- Liquid and dry weights can usually be rounded to a sensible number of grams or millilitres.
- Small amounts such as salt, spices and raising agents may need careful adjustment.
- Whole ingredients such as eggs may not divide neatly.
- Cooking time and pan size do not always scale in the same way as ingredients.
For kitchen use, a mathematically exact result is not always the most practical result.
Convert awkward kitchen units
Use the cooking unit converter when a scaled recipe gives you awkward cups, grams, teaspoons or tablespoons.
Scale factor and ratios
A scale factor keeps the same basic relationship between ingredients. That is why recipe scaling is closely linked to ratios and proportions.
For example, if a dough uses 500g flour and 350ml water, doubling the recipe keeps the same flour-to-water relationship: 1000g flour and 700ml water.
This is useful for bread, sauces, marinades, dressings, batch cooking and any recipe where balance matters.
Scale factor FAQs
What does scale factor mean in cooking?
In cooking, scale factor means the number used to multiply each ingredient when changing a recipe from one serving count or batch size to another.
How do you find the scale factor for a recipe?
Divide the desired servings by the original servings. For example, changing 4 servings to 10 servings gives a scale factor of 10 ÷ 4 = 2.5.
What does a scale factor of 0.5 mean?
A scale factor of 0.5 means the recipe is being halved, so each ingredient amount is multiplied by 0.5.
Can every recipe ingredient be scaled exactly?
No. The maths can be exact, but practical cooking may need rounding or judgement, especially for eggs, spices, raising agents, pan size and cooking time.