Baking Pan Size Conversion Calculator
Swapping a recipe from one pan to another is a surface-area problem, not a guess. The amount of batter that fills a pan scales with the base area, so a slightly bigger pan can need far more batter than its diameter suggests, because area grows with the square of size. This calculator computes the area of your original and target pans, whether round or rectangular, and returns the scale factor and the new batter amount to make. Enter dimensions in inches. Baking time changes with fill depth, so use the scale factor for quantity and verify doneness by eye.
Pan conversion formula
round area = pi * (diameter / 2)^2
rectangular area = length * width
scale factor = new area / original area
new batter = original batter * scale factor
For each pan, enter either a round diameter or both rectangle dimensions; leave the unused fields at zero. The calculator uses whichever shape you filled in.
Pan conversion notes
- Area grows with the square of size, so small diameter changes shift volume a lot.
- A 9 inch round pan is about 63.6 square inches; a 9 by 13 inch pan is 117 square inches.
- Scaling assumes similar fill depth in both pans.
- Adjust baking time: shallower fills bake faster, deeper fills slower.
- Use 1 pi at 3.14159265; the calculator uses the precise value.
Pan conversion: frequently asked questions
How do I convert a recipe to a different pan?
Scale by surface area, not by linear size. Compute the area of the original pan and the area of the new pan, then multiply the recipe quantities by new area divided by original area. A batter that fills a 9 inch round pan needs about 1.27 times as much to fill a 10 inch round pan, because area grows with the square of the radius.
How is round pan area calculated?
Round pan area is pi times the radius squared, where radius is half the pan diameter. A 9 inch round pan has area pi times 4.5 squared, about 63.6 square inches. This calculator computes it for you when you choose the round shape and enter the diameter.
How is rectangular pan area calculated?
Rectangular and square pan area is length times width. A 9 by 13 inch pan is 117 square inches. Enter both dimensions; for a square pan enter the same value twice. The calculator compares the two pans by area to give the scale factor.
Does pan depth matter?
This calculator scales by the surface area of the base, which works when both pans have similar depth and you keep the batter at a similar height. If the new pan is much deeper or shallower, baking time and rise change; adjust the oven time and watch for doneness rather than relying on the area alone.
Will baking time change?
Usually yes. A thinner layer in a larger pan bakes faster; a deeper fill bakes slower. The area scale factor tells you how much batter to make, not the new time. Start checking earlier for a larger, shallower pan and later for a smaller, deeper one.
Official sources
- NIST: Office of Weights and Measures (length and area units).
- NIST: National Institute of Standards and Technology.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.