Pan size recipe scaler.

How to scale a recipe for a different pan

King Arthur Baking compares pans by baking area: multiply length by width for a square or rectangle, and use π × radius² for a round pan. A 9×13 inch pan is 117 square inches, a 9-inch round is about 64 and an 8-inch round about 50. Scaling a recipe is then new area ÷ old area, applied to every ingredient. King Arthur's worked case turns a 9×13 sheet cake into two round layers: two 9-inch rounds hold about 10% more than the rectangle, and two 8-inch rounds about 9% less, so for a new recipe it recommends two 9-inch pans.

Worked example. 117 square inches becomes two 9-inch rounds, 2 × 63.6 = 127.2 square inches, a factor of 1.087. A recipe with 2 cups of flour needs about 2⅛ cups.

Eggs. A scaled recipe often lands between whole eggs. Utah State University Extension gives a raw large egg as about 3 tablespoons, so the tool shows the tablespoons of beaten egg to use for a fraction. Quantities are rounded to the nearest ⅛, which is finer than most measuring cups; use grams or a scale where precision matters. Lines it cannot read (for example "salt to taste" or a range such as "2 to 3") are left unchanged and marked.

The tool treats batter depth as unchanged. If your new pan is shallower or deeper, or you are switching between a cake and a bar, the baking time changes and no formula here predicts it, so check early. For a straight volume comparison of pans, see the baking pan size converter.