How do I convert a recipe from a round cake tin (cake pan) to a square one?
Generally you reduce the round cake tin size by 2 cm (1 inch) to arrive at the equivalent size of square cake tin. So a 20 cm (8 inch) round cake tin can be switched for an 18cm (7 inch) square tin and a 23cm (9 inch) round tin can be switched for a 20 cm (8 inch) square tin.
The cake batter should come roughly half way up the side of the cake tin (round or square) so if there is a lot more or less than this in your tin then the size of the tin may be wrong or the baking time may be different to the one stated in the recipe. Also square tins have sharp corners which burn slightly more easily so if converting from a round to a square tin you may need to rotate the tin more than once to give more even cooking and check that the cake is baked slightly earlier than the recipe suggests.