What do I need to know when I wish to bake a cake or bar recipe in a different size or shape than the recipe calls for?
The most important thing is to make sure that the pan you wish to use holds the same volume and has a similar depth as the pan called for in the recipe.
Remember that using a different pan size requires an adjustment in baking time—a cake baked in a smaller and deeper pan than called for will require a slightly longer time to bake.
To measure a pan’s volume, fill it with water and then measure the liquid. A pan’s width is measured from inside edge to inside edge, and its depth from the bottom of the pan to the rim.