Cake Tin Size Converter
Convert a cake recipe from one tin size to another. Calculate the scale factor for ingredients and adjusted baking time when your tin differs from the recipe.
Cake Tin Conversion Guide
Why Tin Size Matters
The volume (and base area) of a cake tin determines how deep the batter sits and how long it takes to bake through. A recipe for a 20cm round tin used in a 23cm tin spreads thinner and bakes faster. Used in an 18cm tin, the batter sits deeper and needs longer. The base area is what determines ingredient scaling: round tin area = π × (diameter/2)². Square tin area = side × side. A 20cm round (314 cm²) vs a 23cm round (415 cm²) means you need 32% more batter (scale factor 1.32) for the same depth.
Round vs Square Equivalences
Converting between round and square tins: a square tin has approximately 25% more volume than a round tin of the same dimension. So a 20cm square tin ≈ 22–23cm round tin. Common equivalences: 18cm round ≈ 15cm square, 20cm round ≈ 18cm square, 23cm round ≈ 20cm square, 25cm round ≈ 23cm square. For loaf tins: a standard 2lb (900g) loaf tin (23×13×7cm) holds approximately 1.4 litres of batter — equivalent to a 20cm round tin.
Baking Time Adjustments
When scaling up (larger tin): the batter is thinner, so reduce time by 10–20% and check early. When scaling down (smaller tin): the batter is deeper, so increase time by 10–25% and test with a skewer. Temperature usually stays the same. Exception: very deep cakes (Christmas cake, rich fruit cake) may need temperature reduced by 10°C to prevent burning the outside before the inside is done. Multi-layer cakes with thinner individual layers bake 20–30% faster than a single deep cake.
Ingredient Scaling for Baking
All ingredients scale linearly with volume: if the scale factor is 1.3, use 1.3× every ingredient — flour, butter, sugar, eggs, baking powder, liquid. For eggs, the calculation often gives a non-whole number (1.3 eggs). Handle this by: weighing eggs (a large egg is typically 55–60g) and using the appropriate weight, or rounding to the nearest whole egg and adjusting liquid slightly, or using two medium eggs where 1.5 large eggs are needed. Leavening agents (baking powder, bicarb) should be scale
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