How to use it
- Choose the Recipe tin shape and its unit, then enter its diameter, side or length.
- For a rectangular tin, enter its width as well.
- Choose the shape and unit of My tin and enter its size.
- Multiply every ingredient by the Ingredient multiplier, and follow the Baking time note.
How the multiplier is calculated
The inside area of a tin sets how much batter it holds when the batter is the same depth. A round tin has the area of a circle, pi times the radius squared. A square tin is the side times itself and a rectangular tin is length times width. The tool measures both tins in square centimetres and divides the area of your tin by the area of the recipe tin.
round: area = π × (diameter ÷ 2)²
square: area = side × side
rectangle: area = length × width
multiplier = area of your tin ÷ area of the recipe tin- One inch is exactly 2.54 centimetres.
- A multiplier of 1.5 means every ingredient should be 1.5 times as much.
- The multiplier only works when the batter stays the same depth. Fill the pan about halfway to two-thirds full, as the recipe does.
What the baking note means
The baking time depends mainly on how deep the batter is, not on the area of the tin. A tin that is larger spreads the batter thinner, so it bakes sooner. A smaller tin makes a deeper cake that needs more time.
- Within about 1 % of the same area: bake for the time in the recipe and check at the end.
- Larger tin: start checking 10 to 15 minutes before the time in the recipe.
- Smaller tin: add time in 5-minute steps until a skewer comes out clean.
What this converter does not cover
- Tins with a height that differs much from the recipe tin. A tall tin needs more time than the depth suggests, so check with a skewer.
- Ring, bundt, loaf and muffin tins with curved or deep shapes. Their area is not a simple shape, so use the tin's capacity in millilitres where it is printed.
- Oven temperature. This tool changes only the time note; it does not change the heat.
Worked example: 8 inch square to 9 inch round
An 8 inch square tin is 20.32 cm on each side, so its area is 20.32 × 20.32 = 412.9 cm². A 9 inch round tin has a diameter of 22.86 cm, so its radius is 11.43 cm and its area is π × 11.43 × 11.43 = 410.4 cm².
The multiplier is 410.4 ÷ 412.9 = 0.99. The two tins hold almost the same batter, so every ingredient stays as it is and the baking time stays close to the recipe's.
| Recipe tin | Your tin | |
|---|---|---|
| Shape and size | 8 in square | 9 in round |
| Area | 413 cm² | 410 cm² |
| Multiplier | 1 | 0.99 |
Frequently asked questions
How do I convert a cake recipe to a different tin?
Divide the area of your tin by the area of the recipe tin, then multiply each ingredient by that multiplier. This works when the batter is the same depth in both tins.
Why does the baking time change?
The time depends mainly on the depth of the batter. A larger tin makes the batter shallower and it bakes sooner; a smaller tin makes it deeper and it takes longer.
Is a round tin the same size as a square one?
Not by its measurements. A 9 inch round tin has about the same area as an 8 inch square tin, which is why the multiplier in the worked example is close to 1.
Why do the areas use centimetres when I entered inches?
Each tin is converted to centimetres first, using the exact definition of 2.54 centimetres to one inch, so the two tins can be compared on the same scale.
Can I use this for a loaf tin or a bundt pan?
Not as an exact conversion. Those tins have curved or deep shapes that a simple area cannot describe, so use the capacity printed on the tin, in millilitres, and compare that with your recipe.
Sources
- Food Network: baking pan conversion guide (keep the batter depth the same)
- Bakeclub: Adjusting baking times (how batter depth changes the time)
- NIST Handbook 44, Appendix C: 1 inch = 2.54 centimetres (exactly)
Figures and text last checked on Tuesday, November 10, 2026.