Baking Pan Size Converter
Convert between round, square, and rectangular pans. Know exactly how much batter you need.
Why Pan Size Matters in Baking
Using the wrong pan size is one of the most common baking mistakes. A recipe designed for a 9-inch round pan poured into an 8-inch pan will overflow or bake unevenly — the batter is 27% more than the pan can handle.
This calculator uses the actual geometry (π × r² for circles, length × width for rectangles) to compute exact volume differences and gives you the precise scale factor to adjust your recipe.
Common Pan Conversions
The most frequently needed swaps: a 9-inch round has about the same area as an 8-inch square (the math works out almost perfectly). Two 9-inch round layers equal one 9×13 rectangular pan. A 10-inch round is 23% larger than a 9-inch round — not 11% as many people assume.
Adjusting Bake Time for Different Pans
When switching to a larger pan (thinner batter layer), reduce baking time by 5-10 minutes and check early. Smaller pans (thicker layer) need more time — add 5-15 minutes. Always use the toothpick test rather than relying solely on time.
A 10-inch pan has 23% more area than a 9-inch pan, not 11%. People assume the difference is proportional to diameter, but area scales with the square of the radius. This is why your cake overflows when you go "just one inch smaller."
