🥧 Baking Pan Size Converter

Compare your original and target pan sizes to find the area ratio for scaling ingredient amounts and adjusting bake time.

Original Pan

Dimension A (in)

Dimension B (in, rect only)

Target Pan

Dimension A (in)

Dimension B (in, rect only)

It compares floor area, in square inches

Pans are swapped by how much surface the batter spreads over, so the tool works out each pan's area and divides one by the other:

round:       area = π × (diameter / 2)²
rectangular: area = length × width
scale factor = target area / original area

Moving a 9 in round (63.6 sq in) into a 9 x 13 (117 sq in) gives x1.84, so every ingredient goes up by 84%. The reverse direction, x0.54, is the one worth checking twice.

Pan	Area
8 in round	50.3 sq in
9 in round	63.6 sq in
8 x 8 square	64 sq in
9 x 13	117 sq in

What the ratio does not tell you

Area is only half the problem, because the tool never asks how deep your pans are.

Bake time follows depth, not area. Scale the batter properly and the depth stays the same, so the time barely moves. Pour the original batter into a larger pan instead and it bakes as a thinner layer - start checking 25% early.
Fill to about two-thirds. A deep pan with the right area can still overflow, and a cake more than about 2 in deep sets a crust before the middle cooks.
Round up eggs, not everything. A x1.84 scale wants 1.84 eggs. Use two and let the flour take the difference.

Below about x0.5 or above x2, leavening stops behaving. Baking powder and soda react with surface area and depth as well as quantity, so a heavily scaled batter can dome, crack or collapse. Two pans of the original size are safer than one very large one.

Frequently asked questions

Can I use a 9x13 pan instead of two 9 inch rounds?

Yes. Two 9 in rounds are 127 sq in against 117 for a 9 x 13, so the batter sits about 9% deeper. Bake it 5-10 minutes longer and test the middle.

Is an 8 inch square the same as a 9 inch round?

Near enough - 64 sq in versus 63.6, a ratio of 1.01. Swap them with no change to the recipe or the time. The square gives you corner pieces and a little more browning.

Does bake time change when I change pan size?

Only if the depth of the batter changes. Same depth, same time. A shallower layer cooks faster and a deeper one slower, and neither follows the area ratio, so test with a skewer rather than trusting the clock.