What this calculator does
Scaling a recipe by servings is a single multiplication for the ingredients: work out the factor, multiply everything by it. Going from 4 servings to 6 gives a factor of 1.5, so 250 g becomes 375 g. That part is straightforward and rarely goes wrong.
Tin size and cooking time are where scaling actually fails. A doubled cake mixture in the same tin bakes to twice the depth, and depth is what governs how long heat takes to reach the centre. The tin diameter needs to grow as the square root of the factor to keep the depth the same, and even then the time changes rather than staying put. The time figure here is an estimate to start from, not a replacement for checking.
The formula
The scale factor is the servings you want divided by the servings the recipe makes. Every ingredient quantity is multiplied by it. The suggested tin diameter change is the square root of the factor, because a round tin area grows with the square of its diameter and it is area that has to scale for the depth to stay constant. The revised cooking time uses the factor raised to the power 0.4, an empirical rule that reflects time growing much more slowly than volume.
| Term | Meaning |
|---|---|
| Scale factor | New servings divided by original servings, the number every ingredient is multiplied by. |
| Tin diameter change | The square root of the scale factor, which keeps the depth of the mixture unchanged. |
| Cooking time estimate | The original time multiplied by the factor to the power 0.4, a rough empirical adjustment rather than a physical law. |
The inputs explained
| Field | What to enter |
|---|---|
| Original servings | How many servings the recipe as written makes. |
| Servings you want | How many servings you want. |
| An ingredient quantity | One ingredient quantity to rescale. Run the calculator again for each ingredient, or just apply the scale factor yourself once you have it. |
| Original cooking time (minutes) | The cooking time the recipe gives, in minutes. |
When to use it
Cooking for a different number of people
The most common case, and the one where the ingredient arithmetic alone is usually enough, particularly for anything cooked on the hob where timing is judged by eye rather than set in advance.
Scaling a cake or bake up a size
Baking is where the tin and time adjustments matter. Doubling a mixture into the same tin gives a cake that is raw in the middle and overdone at the edges, and the suggested diameter change is what avoids it.
Halving a recipe written for a crowd
Scaling down runs into the same issues in reverse: a shallower mixture cooks faster than the written time and will be dry if left the full duration.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How do ingredients, tin size and time change as a recipe is scaled?
The same recipe scaled from half size up to triple, showing all three adjustments together.
| Servings wanted | Scale factor | That ingredient becomes | Suggested tin diameter change | Approximate new cooking time |
|---|---|---|---|---|
| 2 | 0.500× | 125.00 | 0.71× the diameter | 34 minutes |
| 4 | 1.000× | 250.00 | 1.00× the diameter | 45 minutes |
| 6 | 1.500× | 375.00 | 1.22× the diameter | 53 minutes |
| 8 | 2.000× | 500.00 | 1.41× the diameter | 59 minutes |
| 12 | 3.000× | 750.00 | 1.73× the diameter | 70 minutes |
Questions
Why does doubling a recipe not double the cooking time?
Because cooking time depends on how far heat has to travel to the centre, not on how much food there is. A wider tin holding twice as much has roughly the same depth, so the centre is barely further from the surface. Time grows, but slowly, which is what the power of 0.4 reflects.
How do I scale eggs?
Round to the nearest whole egg and adjust the liquid slightly if the rounding is large. A factor of 1.5 on 3 eggs gives 4.5, so use 4 or 5 depending on which way the rest of the mixture needs to go. Beating an egg and using half by weight works where precision matters.
Should I change the oven temperature?
Generally no. Keep the temperature and adjust the time, checking earlier than the estimate suggests. Dropping the temperature by 10 to 20 degrees can help for a much larger bake that is browning before the centre is done, but that is a fix for a specific problem rather than a default.
Do seasonings scale in proportion?
Not reliably. Salt scales close to proportionally, but strong spices, chilli and anything bitter tend to scale up more intensely than the factor suggests. Scaling those at slightly less than the factor and adjusting at the end is safer, since more can be added and none can be removed.
For scaling a concentrate against a solvent rather than a recipe, see the dilution ratio calculator. For a brew ratio worked the same way, see the coffee brew ratio calculator.