BAKING NOTE
8-inch to 9-inch cake pan conversion
For the same number of straight-sided round pans and the same batter depth, multiply every ingredient by 1.265625 when moving from an 8-inch pan to a 9-inch pan. That is about 26.6% more batter.
1.265625×
New amount = original amount × 81 ÷ 64
Set up the 8-to-9-inch recipe calculator →Apply the pan settings in the calculator, then enter your recipe. Your existing ingredient list stays intact.
TRY YOUR OWN NUMBERS
Calculate right here
Enter your measurements and ingredient weights. This example illustrates the math; it is not a tested recipe.
Your scaled amounts
| Ingredient | Original | Scaled |
|---|
These inputs stay on this page and clear on reload. Your saved recipes and working draft are unchanged. Use the full calculator to save a recipe or download it.
Why the multiplier is not 9 ÷ 8
Diameter grows by 12.5%, but a round pan’s base area grows with the square of its diameter. At equal batter depth, compare areas: π × 4.5² ÷ (π × 4²) = 81 ÷ 64 = 1.265625. Use measured inside dimensions; the size printed on the packaging may differ from the usable base.
Ingredient conversion example
This is an arithmetic illustration, not a tested cake recipe. Multiply the weights in your own complete recipe by the same factor. Values below are rounded to 0.1 g; the calculator retains full precision.
| Ingredient | Original | Scaled (×81/64) |
|---|---|---|
| Flour | 200 g | 253.1 g |
| Sugar | 160 g | 202.5 g |
| Butter | 120 g | 151.9 g |
| Egg, weighed | 100 g | 126.6 g |
For eggs, weigh the edible portion without shells. If a scaled quantity needs part of an egg, mix the egg and weigh the required amount where appropriate for your recipe. Do not treat every egg as an identical weight.
What if the recipe makes more than one layer?
Include the number of pans, not just their diameters. Two 8-inch pans to two 9-inch pans still uses 1.265625×. Two 8-inch pans to one 9-inch pan uses half that factor: 0.6328125×. This describes the same batter depth per pan, not the same number of finished servings.
| Original pans | New pans | Multiplier |
|---|---|---|
| 1 × 8-inch | 1 × 9-inch | 1.265625 |
| 2 × 8-inch | 2 × 9-inch | 1.265625 |
| 2 × 8-inch | 1 × 9-inch | 0.6328125 |
Converting a 9-inch recipe to an 8-inch pan
Reverse the ratio: 64 ÷ 81 = 0.790123…. Use about 79.0% of each ingredient, or about 21.0% less. Do not subtract 26.6%: reversing a ratio is division, not reversing a percentage increase.
Set up the reverse 9-to-8-inch conversion →
Can I leave the recipe unchanged?
If you spread the same batter into the larger pan, the starting depth is about 79.0% of the original under this straight-sided model. The finished cake height and baking time do not follow directly from that number. Changing pan size, material, oven conditions and batter depth can affect the bake.
Check depth and doneness separately
The ratio assumes the same actual batter depth, not that both pans must have equal wall heights. Leave the rise space required by your recipe. If you deliberately change batter depth, use the calculator’s depth option and review the recipe’s baking guidance. Do not multiply oven temperature or baking time by 1.265625.
Bundt pans, tube pans and sloped or irregular pans need a capacity-based approach outside this model. For a different shape, see round-to-square pan conversion. For limited ingredients, use available-ingredient scaling.
Method and further reading
The examples use circle area and proportional ingredient weights; they have not been bake-tested. For practical context, read King Arthur Baking’s explanation of why pan size matters. See the full calculator guide for saving, copying and handling small weights.