Cake Tin Converter
Convert cake tin sizes — round to square, and between different diameters. Adjust recipe quantities when changing tin sizes. Free cake tin converter.
Closest Equivalent
Round tin
20cm
314cm²
Square tin
18cm
324cm²
Area difference: +3%
Scale up recipe by 3%. The new tin holds more batter.
Baking time should be approximately the same.
Round ↔ Square Equivalents
| Round tin | Square equivalent | Area diff |
|---|---|---|
| 15cm round | 13cm square | -4% |
| 18cm round | 15cm square | -12% |
| 20cm round | 18cm square | +3% |
| 23cm round | 20cm square | -4% |
| 25cm round | 23cm square | +8% |
| 28cm round | 25cm square | +2% |
How to use this tool
Select the tin you have
Choose round or square and the tin size from the buttons. Common UK sizes (18cm, 20cm, 23cm) are pre-set for quick selection.
Select the tin your recipe calls for
Choose the target shape and size. The converter calculates the area difference and shows the batter quantity adjustment needed.
Adjust your recipe and timing
The result shows the scaling factor for your batter quantities, plus guidance on baking time and temperature adjustments for the new tin.
Tips
Always weigh batter into tins rather than guessing by eye — this ensures even layers and accurate conversions.
Line tins with baking parchment regardless of non-stick coating. Parchment guarantees clean release and protects the tin.
When in doubt, use a lower temperature (10°C less) for a slightly longer time — cakes are forgiving of gentle heat, not of burning.
If converting to a significantly deeper tin, cover the top with foil for the first two-thirds of baking to stop the surface burning before the centre is set.
About this cake tin converter tool
Cake tin sizes follow no universal standard, and recipe writers rarely specify what to do if you don't have the exact tin. The solution is simple: compare the base area of the two tins. If your tin has a larger area than the recipe specifies, the same batter fills it to a shallower depth — baking faster and producing a flatter cake. A smaller tin means deeper batter and longer baking.
Round and square tins of the same nominal size hold different volumes. A 20cm square tin has a base area of 400cm², while a 20cm round tin has a base area of only 314cm² — about 21% less. This is why substituting a square tin for round without adjustment produces a thinner cake. The correct substitution is to use a square tin 2–3cm smaller than the round tin specified.
Baking time adjustments are the trickier part. The general principle: a larger tin means shallower batter, which bakes faster. Reduce oven temperature by 10°C and start testing 10–15 minutes before the original recipe time. For very significant size differences, increase batter quantity to maintain the correct depth rather than baking a very thin cake.
Many experienced bakers keep a set of three round tins (18cm, 20cm, 23cm) and a 20cm square tin, which covers the vast majority of UK recipe requirements. With this tool and a basic understanding of the area relationship, you can confidently adapt any recipe to any tin you have.