Cake Pan Size Converter
Convert any cake recipe to a different pan size and get an adjusted baking time instantly. Use this when substituting a 9-inch round for a 8-inch square or any other pan swap.
About this calculator
When you change pan size, the batter depth changes, which directly affects how long heat takes to reach the center of the cake. The adjusted bake time formula is: newBakeTime = originalBakeTime × (newPanSize / originalPanSize)² × (newDepth / originalDepth). The squared term accounts for the change in cross-sectional area — a larger pan spreads batter thinner, reducing bake time, while a smaller pan concentrates batter deeper, increasing it. The depth ratio then fine-tunes the result for pans with different wall heights. Temperature generally stays the same, but you may lower it by 25°F for very deep pans to prevent overbaking the edges before the center sets.
How to use
Suppose your recipe calls for a 9-inch pan, 2 inches deep, with a 35-minute bake time, and you want to use an 8-inch pan that is 3 inches deep. Plug in: newBakeTime = 35 × (8/9)² × (3/2) = 35 × 0.790 × 1.5 = 41.5 minutes. So you would bake the cake for approximately 42 minutes. Always start checking for doneness a few minutes early by inserting a toothpick — it should come out clean when the cake is done.
Frequently asked questions
How do I convert a 9x13 inch pan recipe to two 9-inch round pans?
A 9×13 pan has an area of 117 square inches, while two 9-inch rounds together offer about 127 square inches. The volumes are close enough that you can use roughly the same bake time, but start checking 5 minutes earlier since the batter will be slightly shallower. Watch for the edges pulling away from the pan and use the toothpick test to confirm doneness. Baking temperature remains unchanged.
Why does changing pan size affect baking time so much?
Heat transfers from the outside of the batter inward, so the distance from the pan wall to the center of the batter determines how long baking takes. A larger pan spreads batter into a thinner layer, shortening the path heat must travel and reducing bake time. Conversely, a smaller or deeper pan increases that distance, requiring more time. The relationship is roughly proportional to the square of the size ratio for diameter changes, plus a linear factor for depth.
Should I change the oven temperature when using a different pan size?
In most cases you keep the same temperature, but there are exceptions. For very deep pans or dense batters, reducing the temperature by 25°F (about 15°C) helps the center cook through without the exterior over-browning. For very shallow pans or thin layers like sheet cakes, the original temperature is usually fine but bake time drops significantly. Always monitor visually and use a toothpick or cake tester rather than relying on time alone.