Baking Pan Size Converter
How much to scale a recipe for a different cake tin or baking pan.
Good to know. A 23 cm round tin holds about a third more than a 20 cm one. The difference is squared, not added.
How it works
In plain words
A recipe fills a tin by area, so work out each tin’s base area: π × radius² for a round tin, side × side for a square one and length × width for a rectangle. Divide your tin’s area by the recipe’s for the factor.
The formula
round = π × (diameter ÷ 2)² · square = side² · rectangle = length × width factor = your tin’s area ÷ recipe tin’s area
Worked example
A 20 cm round tin has an area of 314.2 cm², a 23 cm one 415.5 cm². 415.5 ÷ 314.2 = 1.32, so multiply every ingredient by 1.32.
Sources
No outside data or rates: this is plain arithmetic.
4 automated tests check its answers on every change.
About the baking pan size converter
Recipes are written for one tin, and your cupboard often has another. To keep the cake the same depth, scale the recipe by the ratio of the two tins’ base areas. This calculator works that out for round, square and rectangular tins, in centimetres or inches.
Area grows with the square of the size, so small changes in diameter matter: a 23 cm round tin is 32% larger than a 20 cm one, and a 25 cm tin 56% larger. Round and square tins of the same width differ too: a square tin holds about 27% more than a round one of the same size. As a rule of thumb, a 20 cm (8 in) square tin takes about the same mixture as a 23 cm (9 in) round tin.
Multiply every ingredient by the factor. For eggs, round to the nearest whole egg, or beat an extra one and use part of it. The recipe scaler does the arithmetic for a whole ingredient list: enter the factor as the ratio of servings.
Baking time changes with depth more than with size. In a larger tin at the same depth, the time stays similar, but check a little early; if you don’t scale the recipe up, the cake will be thinner and bake faster. A deeper cake needs longer, sometimes at 10–20 °C lower so the outside doesn’t burn before the middle is done.
Questions people ask
How do I convert a recipe from a round to a square tin?
Compare the areas. A 20 cm square tin (400 cm²) holds about the same as a 23 cm round tin (415 cm²).
How much bigger is a 9 inch pan than an 8 inch pan?
A 9 inch round pan has about 27% more area than an 8 inch round pan, so multiply the recipe by about 1.27.
What can I use instead of a 9 × 13 inch pan?
Two 8 inch square pans (128 in² together) are close to a 9 × 13 (117 in²), or two 9 inch round pans.