Baking-tin conversion calculator
Compare straight-sided round or rectangular tins at the same batter depth. Use internal dimensions and the same unit throughout.
Original tin
New tin
This is an area comparison, not a capacity or baking-time calculation. Check that the new tin is deep enough and has room for the cake to rise. Not suitable for tapered loaf tins, ring tins or Bundt moulds. For big changes, choose a recipe developed for your tin.
You have a recipe for a 20 cm round cake tin, but the tin in your cupboard is 23 cm. How much mixture should you make?
For straight-sided round, square or rectangular tins, comparing the base areas gives a useful starting point when you want to maintain approximately the same batter depth.
This calculation adjusts ingredient quantities. It does not calculate a reliable baking time.
Round tins: Compare the diameters
For two round tins:
Multiplier = new diameter² ÷ original diameter²
You don’t need to calculate pi because it cancels out.
Example: 20 cm to 23 cm
23 × 23 = 529
20 × 20 = 400
529 ÷ 400 = 1.3225
Multiply the original ingredients by approximately 1.32.
An original quantity of 200 g flour becomes approximately 265 g.
Square and rectangular tins
Calculate the base area by multiplying length by width.
Multiplier = new base area ÷ original base area
A 20 × 20 cm tin has a base area of 400 cm². A 20 × 30 cm tin has a base area of 600 cm².
600 ÷ 400 = 1.5, so multiply ingredients by 1.5 to aim for a similar batter depth.
Round-to-square conversions
For a round tin, calculate the base area using:
3.1416 × radius × radius
The radius is half the diameter.
A 20 cm round tin has a base area of approximately 314 cm². A 20 cm square tin has an area of 400 cm².
The square tin therefore needs about 1.27 times the mixture to reach a similar depth.
Check the tin depth too
A matching base area does not guarantee enough capacity. The new tin must also have suitable depth and room for the mixture to rise.
Use internal measurements. These calculations are less useful for tapered loaf tins, ring tins, Bundt tins and unusually shaped moulds.
What about baking time?
Do not multiply the baking time by the ingredient multiplier. Tin material, shape and the recipe itself affect baking.
Use the recipe’s own doneness checks, and choose a recipe written for your tin when making a substantial change or baking something delicate.
Further reading: King Arthur Baking’s guide to baking pans.
