Baking tin sizes: how to swap tins without ruining a recipe

6 minute read · updated 2026-11-01

Quick answer: Compare the area of the tins, not the width. A 23 cm round tin holds about a third more than a 20 cm one, so multiply the recipe by 1.3. A square tin holds the same as a round tin about 11% wider: an 18 cm square matches a 20 cm round. Tin sizes are below.

A recipe written for a 9 inch tin will work in your 20 cm tin, but not without a little thought. The width of a tin sounds like a small difference, but the amount of batter it holds depends on its area, and area grows much faster than width.

Inches and centimetres

Tins are sold in rounded sizes, so the usual equivalents are not exact conversions. These are the matches cooks use.

Inches	Centimetres
6 in	15 cm
7 in	18 cm
8 in	20 cm
9 in	23 cm
10 in	25 cm
11 in	28 cm
12 in	30 cm

Scaling a recipe to a different tin

For round tins, divide the new diameter by the old one and square the result. That is how much more or less batter you need.

20 cm to 23 cm: 23 ÷ 20 = 1.15, and 1.15 × 1.15 = about 1.3. Make a third more mixture.
23 cm to 20 cm: the other way round, about three quarters of the mixture.
20 cm to 25 cm: about one and a half times the mixture.

For square and rectangular tins, multiply length by width for each tin and compare the two areas the same way.

Round tins and square tins

A square tin holds more than a round tin of the same width, because it fills the corners. A square tin with sides about 89 per cent of the round tin's diameter holds the same amount: an 18 cm square matches a 20 cm round, and a 20 cm square matches a 23 cm round.

Depth and baking time

If you keep the same amount of mixture in a wider tin, the cake is shallower and bakes faster, so start checking 10 minutes early. In a smaller, deeper tin it needs longer and may need the oven turning down by 10 °C so the outside does not burn before the middle sets. Fill tins no more than two thirds full. A skewer pushed into the middle should come out clean.

Loaf tins

British loaf tins are sold by the weight of bread they make. A 2 lb loaf tin is roughly the same as an American 9 × 5 inch loaf pan, about 23 × 13 cm, and a 1 lb tin is roughly half its volume. Brands vary, so measure the inside of the base if a recipe is fussy.