Cake Pan Size Converter
How much to scale a recipe when your pan is a different size or shape.
How pan conversion works
If the batter depth stays the same, the amount of batter scales with the pan's surface area. A round pan's area is π × diameter² / 4; a rectangular pan is length × width. Divide your pan's area by the recipe pan's area and that is the factor for every ingredient. Going from a 20 cm round to a 23 cm round is ×1.32, almost exactly a third more batter.
Common swaps
A 20 cm (8 in) round and an 18 cm (7 in) square hold nearly the same. A 23 cm (9 in) round is about 1.3× a 20 cm round. Two 20 cm rounds equal one 23×33 cm (9×13 in) sheet, near enough. A 20 cm round recipe fits a standard loaf pan with a taller rise and a longer bake.
Watch the depth and the clock
Scaling within about 25% works without fuss. Beyond that, the depth changes enough to move the baking time: shallower bakes faster and dries out sooner, deeper needs longer at the same temperature, never a hotter oven. For delicate sponges it is safer to keep the recipe and choose the closer pan.