Cake Tin Conversion Calculator
Recipes specify a tin and nobody has that tin. The instinct is to scale by the diameter, which is badly wrong: a 23cm round tin holds nearly half as much again as a 20cm one, because area goes as the square of the radius. Scale by diameter and the batter either overflows or comes out as a biscuit.
What this generator does
Works out the area of both tins, takes the ratio, multiplies every ingredient by it, and reports how deep the batter will sit in the new tin.
How to use this tool
- Pick the shape and size of the tin the recipe wants.
- Pick the shape and size of the one you have.
- Paste the ingredients, one a line, amount first.
- Read the multiplier and the rescaled list.
Understanding the controls
- Tin the recipe wants
- Round by diameter, square by side, or rectangular and loaf tins by two sides. Shapes can be mixed freely — a round recipe in a square tin is just a ratio of areas.
- Tin you have
- The same choices for the tin actually in the cupboard. Measure across the base rather than the rim, which is often wider.
- Depth of each tin
- Used only when you ask to fill the new tin to the same depth. Otherwise the batter keeps the depth the recipe intended, which is usually what you want.
- Fill my tin to the same depth
- Off, the batter sits at the depth the original recipe gave, so the cake is the same thickness and bakes in the same time. On, the mixture is scaled by volume to fill the new tin, which makes a deeper cake that needs longer.
- The recipe
- One ingredient a line, amount first — “225 g flour”, “4 eggs”. Anything not recognised as a number is left as it is, so notes survive.
Common use cases
- Baking a 20cm recipe in the 23cm tin you own
- Moving a round recipe into a square tin
- Working out whether a loaf tin will take a cake mixture
- Scaling a tray bake up for a bigger tin
- Knowing whether the baking time needs to change at all
How this generator works
The ratio comes from area, not diameter, which is the entire point: going from a 20cm to a 23cm round tin is 1.15 times across but 1.32 times the area. Scaling by area keeps the batter at the depth the recipe intended, so the baking time is unchanged; scaling by volume fills the new tin and makes a deeper cake, which needs longer. The check inverts the conversion — the rescaled recipe is converted back to the original tin and must return the quantities that went in, to the gram — and confirms that every ingredient moved by exactly the same factor, so the recipe stays in proportion.
Randomness and fairness
Nothing is random. The same two tins always give the same multiplier.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Eggs do not divide neatly; round to a whole egg and adjust the liquid if you must.
- Very large changes in size change how a cake bakes as well as how much there is — a much wider, shallower cake browns faster.
- Baking times here are a proportional guide, not a substitute for a skewer.
- Tin depth is the tin, not the batter; most cakes are baked well below the rim.
Privacy and your data
The recipe is rescaled in your browser. Nothing you paste is transmitted or stored.
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