Cake tin size converter: round and square

To bake in a different tin, scale the ingredients by the ratio of the areas: area of your tin ÷ area of the recipe’s tin. From 20 to 23 cm you need 32% more, so all ingredients × 1.32.

Ingredients times

× 1.16 factor

16% more of everything

Area in the recipe: 531 cm²
Area of your tin: 616 cm²
200 g flour becomes: 232 g
3 eggs become: 3.5 eggs

Round eggs to whole eggs. For half an egg, beat one and use half.

If the batter is as deep as before, the baking time hardly changes. Use the skewer test anyway.

Your tins

The calculator asks for:

Tin in the recipe (Round, Rectangular)
Diameter (cm)
Length (cm)
Width (cm)
Your tin (Round, Rectangular)

The calculation runs in your browser. Your details are not saved and not sent anywhere.

Round tin chart

Factor for all ingredients: row = tin in the recipe, column = your tin.

Round tins from 18 to 28 cm
Recipe	18 cm	20 cm	22 cm	24 cm	26 cm	28 cm
18 cm	1.00	1.23	1.49	1.78	2.09	2.42
20 cm	0.81	1.00	1.21	1.44	1.69	1.96
22 cm	0.67	0.83	1.00	1.19	1.40	1.62
24 cm	0.56	0.69	0.84	1.00	1.17	1.36
26 cm	0.48	0.59	0.72	0.85	1.00	1.16
28 cm	0.41	0.51	0.62	0.73	0.86	1.00

Square and round

Rectangular tins compared with a 20 cm round tin
Rectangular tin	Area	Same as round	Factor from 20 cm
20 × 20 cm	400 cm²	23 cm	1.27
23 × 23 cm	529 cm²	26 cm	1.68
30 × 20 cm	600 cm²	28 cm	1.91
33 × 23 cm	759 cm²	31 cm	2.42

How the calculator works

Round tin: area = π × (diameter ÷ 2)². Rectangular tin: length × width.
Factor = area of your tin ÷ area of the recipe’s tin, to two decimal places. With all ingredients times this factor, the batter is just as deep.
In the example rows the calculator rounds grams to whole numbers and eggs to halves.

Example: Recipe for a 20 cm round tin, yours is 23 cm:

20 cm: 3.14 × 10 × 10 = 314 cm²
23 cm: 3.14 × 11.5 × 11.5 = 415 cm²
415 ÷ 314 = 1.32: all ingredients × 1.32

Good to know

Round eggs to whole eggs. For half an egg, beat one and use half.
If the batter is as deep as before, the baking time hardly changes. Deeper batter takes longer – use the skewer test.
A 33 × 23 cm traybake tin holds 1.83 times as much as a 23 cm round tin.

Frequently asked questions

How do I convert a 20 cm tin to 23 cm?

All ingredients × 1.32. 200 g flour becomes 264 g.

And from 23 cm to 20 cm?

All ingredients × 0.76, about a quarter less.

How do I convert a round tin to a square one?

Work out both areas: round π × radius², square length × width. Then new area ÷ old area. The calculator above does it for you.

What do I do with the eggs?

Round to whole eggs. For half an egg, beat one and use half – the rest can go on top as a glaze.

Does the baking time change?

Hardly, if the batter is as deep as before. Deeper batter takes longer, shallower is quicker. Use the skewer test.

Updated 22 October 2026