It's all about surface area, not the label
When you swap one pan for another, the number that actually matters is the surface area, because that's what sets how deep the batter sits and therefore how it bakes. For a round pan the area is π × radius²; for square and rectangular pans it's simply width × length. Comparing areas tells you the true ratio between two pans — which is exactly what this converter calculates so you can scale a recipe with confidence instead of guessing.
Pans that are closer than they look
Some classic swaps work because the areas land almost on top of each other. A 9-inch round pan and an 8-inch square pan have nearly the same surface area, so they're broadly interchangeable. Two 8-inch round layers add up to roughly the same area as a single 9×13-inch rectangle, which is handy when you want a sheet cake instead of a layer cake. The converter spells these out with real numbers, but it's useful to know a couple by heart for quick decisions at the store or mid-recipe.
Adjusting the recipe to the new pan
Once you know the area ratio, you scale the ingredients by it. Moving to a pan with 20% more area means multiplying the recipe by about 1.2 to keep the same batter depth; moving to a smaller pan means scaling down so it doesn't overflow. If you'd rather keep the original recipe amount and just use a different pan, expect a thinner or thicker bake instead — which then changes the time. Either approach is fine; the key is deciding whether you're matching the depth or matching the quantity.
Depth changes the bake time and temperature
A bigger pan spreads batter thinner, so it bakes faster and can dry out at the edges if you're not watching. A smaller pan makes a thicker, deeper bake that needs more time — and often a slightly lower temperature — so the center sets before the outside overbrowns. As a rough guide, adding or removing 5–10 minutes covers many swaps, but lean on doneness cues (a clean skewer, a springy top, the edges pulling away) rather than the clock. Fill pans only about half to two-thirds full so there's room to rise; bake any extra batter as cupcakes.
Material and color matter too
Two pans of identical size can still bake differently depending on what they're made of. Dark metal absorbs more heat and browns the bottom and sides faster, so it's worth dropping the temperature by around 25°F or shortening the time. Glass and ceramic heat slowly but hold heat well, also leaning toward more browning. Light, shiny aluminum is the gentle middle ground many bakers default to. None of this is captured by area alone, so once the converter has handled the math, give the material a thought before you commit to a time and temperature.