Compare baking-pan surface areas and estimate a recipe scaling factor between common pan shapes.
Method
Round pan area = π × (diameter ÷ 2)². Square area = side². Rectangle area = width × length. Recipe multiplier = target area ÷ original area.
Example: A 9-inch round pan and an 8-inch square pan have nearly the same surface area, so the multiplier is about 1.01.
Limitation
This compares top surface area only. Pan depth, batter type, fill level and baking time can still require recipe-specific adjustments.