Original visual accompanying the guide: Round to Rectangular Cake Pans: Scale by Area
Compare areas for equal batter depth
An eight-inch round pan has area π × 4², or about 50.27 square inches. A 9-by-13-inch rectangle has area 117 square inches. Dividing 117 by 50.27 gives about 2.328. To maintain roughly the same batter depth in the larger pan, multiply the recipe ingredients by that factor. Use interior dimensions and the same unit throughout.
Decide what to do with fractional ingredients
A scaling factor rarely turns every ingredient into a convenient whole number. Weigh beaten egg when a recipe adjustment requires part of an egg, and use a suitable scale for small quantities. Where a recipe is unusually sensitive to leavening or mixing, a tested recipe for the target pan is preferable. Geometry supplies a quantity ratio, not a complete baking method.
Do not scale baking time by the area factor
Multiplying ingredient amounts by 2.328 does not mean multiplying oven time by 2.328. Pan material, shape and batter depth affect the bake. Start checking with the recipe's doneness cues and account for any changed depth. A center that remains wet while the edge overbakes calls for a different baking approach, not blind reliance on an area calculation.
Work out your quantity
Use the Cake Pan Converter with the assumptions described above. Browse Food calculators for another kitchen conversion, or visit GreenCalc for the full calculator library.
Related guide: Measure Cake Pans Inside: Depth, Fill and Overflow.
By GreenCalc · Updated 2026-11-03