Cake Pan Conversion Calculator
Adjust a recipe when swapping to a different size or shape of tin.
Please note: An estimate based on the figures you entered. Real-world results vary with conditions this calculation cannot see, so treat it as a starting point rather than a final answer.
What the Cake Pan Conversion Calculator does
Swapping tins is a question of area, not diameter. Because area grows with the square of the radius, a 9 inch round tin holds a quarter more than an 8 inch one — which is why a recipe poured straight across comes out too shallow.
Formula
Round area = π × (diameter ÷ 2)²Square area = side²Rectangular area = width × lengthScaling factor = New area ÷ Original area
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Original tin shape | one of 3 options | Yes | — |
| Original diameter or width | number | Yes | Accepts more than 0. |
| Original length | number | In some modes | Accepts more than 0. Shown in 3 of the 9 modes. |
| New tin shape | one of 3 options | Yes | — |
| New diameter or width | number | Yes | Accepts more than 0. |
| New length | number | In some modes | Accepts more than 0. Shown in 3 of the 9 modes. |
| Dimensions in | one of 2 options | Yes | — |
| Original baking time | minutes | Optional | Accepts 0 or more. |
How to use it
- Choose Original tin shape and New tin shape.
- Enter Original diameter or width and New diameter or width.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Original baking time.
- Select Calculate.
Worked example
Moving a recipe from an 8 inch round tin to a 9 inch round.
- Original
- 8 inch round
- New
- 9 inch round
Areas are 50.27 in² and 63.62 in², so the factor is 1.266. Scale the recipe up by about a quarter, or accept a shallower cake.
Frequently asked questions
Why does one inch make so much difference?
Area scales with the square of the diameter. Going from 8 to 9 inches is only 12.5% wider but 26.6% more area, and the batter has to cover all of it.
Can I use a square tin instead of round?
Yes, but a square tin of the same nominal size holds about 27% more. Either scale the recipe up or expect a shallower, faster-baking cake.