Baking Tin Converter
Scales by area, which is the step most people skip.
Area, not diameter
A 20 cm round tin and a 23 cm one sound close. They are not: area goes up with the square of the radius, so the larger tin holds 32 % more.
Pour a 20 cm recipe into a 23 cm tin and the batter is a quarter shallower. It bakes faster, browns more, and comes out flatter and drier than it should.
Common tins and their areas
- 15 cm round — 177 cm²
- 18 cm round — 254 cm²
- 20 cm round — 314 cm²
- 23 cm round — 415 cm²
- 20 cm square — 400 cm²
- 23 cm square — 529 cm²
- 23 × 33 cm tray — 759 cm²
Two useful equivalences fall out of that: a 20 cm square holds about the same as a 23 cm round, and a 23 cm square is close to two 20 cm rounds. Those are worth remembering, because they let you substitute without any arithmetic.
Adjusting the bake
- Shallower batter — check 10–15 minutes early. It will be done sooner than the recipe says.
- Deeper batter — add time, and consider dropping the temperature 10–20 °C so the middle sets before the outside overcooks.
- Fill no more than two-thirds. Cake needs room to rise, and batter over the edge is not recoverable.
Depth matters as much as area
Tins of the same width vary in height, and a deep tin genuinely holds more. If yours are unusually shallow or deep, the area calculation is a starting point rather than the final word — judge by how full it looks.
Loaf tins are the least standardised
"1 lb" and "2 lb" loaf tins vary noticeably between manufacturers. If you need to know what yours holds, fill it with water and measure: a 2 lb tin is usually around 1.5 litres.
Common uses
- Using the tin you own rather than buying another.
- Converting between round and square.
- Scaling a recipe to fill a tin properly.
- Splitting a batch across two tins.
The working, step by step
Questions people ask
How do I convert between tin sizes?
By area, not diameter. A 23 cm round tin holds 32 % more than a 20 cm one, because area goes up with the square of the radius.
What size round tin equals a 20 cm square?
About 23 cm round. A 20 cm square is 400 cm² and a 23 cm round is 415 cm² — close enough.
How full should I fill a cake tin?
No more than two-thirds. Cake needs room to rise and overflow cannot be recovered.
Do I need to change the baking time?
Yes. Shallower batter cooks faster — check 10–15 minutes early. Deeper batter needs longer and often a slightly lower temperature.
Why do loaf tins vary so much?
Because 1 lb and 2 lb are nominal rather than standardised. Fill yours with water to find out what it really holds — a 2 lb tin is usually around 1.5 litres.
Worked out in the page
The arithmetic runs in your browser. Nothing you type is sent anywhere, and the site works with no connection once the page has loaded — which is the point when you are in a kitchen with floury hands and a patchy signal.