Cake Tin Converter
Convert cake recipes between different tin sizes and shapes. Round to square, 8 inch to 10 inch — get the exact ingredient multiplier and adjusted baking times.
Your Tin
Recipe Tin
Shape Visualisation
Scaling factor
1.32x
Ingredient Scaling
Based on a standard Victoria sponge recipe
| Ingredient | Original | Scaled |
|---|---|---|
| Plain flour (g) | 225 | 298 |
| Caster sugar (g) | 225 | 298 |
| Butter (g) | 225 | 298 |
| Eggs | 4 | 5 to 6 |
| Milk (ml) | 150 | 198 |
| Baking powder (tsp) | 2.0 | 2.6 |
| Cocoa powder (g) | 40 | 53 |
| Vanilla extract (tsp) | 1.0 | 1.3 |
Baking time adjustment
Original recipe time x 0.95
Larger tin, check earlier
Tips
Fill tins about two-thirds full for the best rise. Overfilling causes spillage, underfilling gives a flat result.
Temperature stays the same when changing tin size. Only the ingredients and baking time need adjusting.
Always check doneness with a skewer 5 minutes before the calculated time, especially with unfamiliar tin sizes.
Deep tins (3") need lower temperature and longer baking to cook through without burning the outside.
Scale a Recipe Between Tin Sizes Without Guesswork
The recipe is for a 23cm (9 inch) round tin. You only have a 20cm (8 inch) round. Or the recipe is for a square brownie tin and you need to bake it round. Tin conversion is a maths problem, not a guess: calculate the surface area of each tin, divide one by the other, and that gives you the multiplier for every ingredient. A 20cm round has an area of 314 cm², a 23cm round has 415 cm², so to scale up you multiply everything by 1.32.
This converter does the area maths for round, square and rectangular tins, then applies the scale factor to a standard Victoria sponge recipe (225g flour, 225g sugar, 225g butter, 4 eggs) so you can see exactly what your scaled quantities should be. Switch between metric and US cup measurements with the toggle. The visual diagram overlays your tin with the recipe tin so you can see at a glance whether you are scaling up or down, and by how much.
Round to Square and the Inch Rule
Common bakers' shorthand: a round tin and a square tin of the same dimension are not the same volume. An 8 inch (20cm) square tin holds 25% more batter than an 8 inch round, because the corners add area. The traditional swap is to go down one inch when moving from round to square: an 8 inch round recipe fits a 7 inch square (around 18cm), a 9 inch round fits an 8 inch square. The calculator confirms this with exact maths so you do not have to remember the rule.
Baking time changes too, but less dramatically than ingredients do. A larger, shallower bake cooks faster because more surface area is exposed; a smaller, deeper one cooks slower. The tool gives you a time multiplier (typically 0.85 to 1.0 in either direction) but always check with a skewer 5 minutes before the calculated time. Oven temperatures stay the same; only the time and quantities adjust.
Common Round Cake Tin Conversions
| From | To | Multiplier | Notes |
|---|---|---|---|
| 15cm (6") | 20cm (8") | 1.78 | Roughly double quantities |
| 18cm (7") | 20cm (8") | 1.23 | Add 23% to ingredients |
| 20cm (8") | 23cm (9") | 1.32 | Add a third |
| 20cm (8") | 25cm (10") | 1.56 | Half again as much |
| 23cm (9") | 25cm (10") | 1.18 | Add 18% |
| 20cm round | 20cm square | 1.27 | Square holds more |
Why Egg Counts Get Awkward
Multiplying flour by 1.32 is fine. Multiplying eggs by 1.32 gives you 5.28 eggs, which is a problem because eggs come whole. The calculator rounds to the nearest whole number where the decimal is below 0.25 or above 0.75 and gives a range otherwise (4 to 5 eggs at 4.5). If you are scaling up, round up; if scaling down, round down and add a splash of milk if the batter looks dry. For tiered wedding cakes where each layer is a different size, see the [recipe scaler](/recipe-scaler) which handles serving counts directly rather than tin areas.
Frequently Asked Questions
Can I use a smaller tin if I reduce the recipe?
Yes, this is exactly what the calculator handles. Scaling down is generally safer than scaling up because there is less risk of the batter being too deep to cook through. If your scaled-down quantities give you awkward fractions of eggs, halve the recipe and bake the leftover batter as cupcakes alongside.
Do I adjust oven temperature when changing tin size?
No, only the cooking time and ingredient quantities change. The oven temperature stays the same because that is what determines how the cake sets and browns. The exception is very deep tins (3 inches and above), which benefit from a 10 to 15°C drop in temperature so the outside does not burn before the centre cooks through.
How full should I fill a cake tin?
Two-thirds full is the standard target for a sponge cake. Fill it any higher and the batter spills over the sides during baking; any lower and the rise is flat and the cake looks underwhelming. The calculator's scaled quantities assume a two-thirds fill at standard 5cm (2 inch) tin depth.
What about loaf tins and bundt tins?
Loaf tins are roughly equivalent to rectangular tins, calculate the rectangular area and use the multiplier directly. Bundt and ring tins are trickier because the central hole reduces the volume; as a rough rule, a 25cm (10 inch) bundt holds about the same batter as a 23cm (9 inch) round cake tin.
Related Tools
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