Cake Recipe Scaling Calculator
Scale a cake recipe between pan sizes and layer counts.
Gives the ingredient multiplier plus scaled flour and eggs, with egg weights for fractions.
Scaling a cake recipe to different pans is an area problem, not a volume one. Almost every cake pan you own is 2 inches deep, so the depth cancels out and what is left is the ratio of the two surface areas. Match that ratio and the batter sits at the depth the recipe was written for.
The formula
Scale factor = total new pan area ÷ total original pan area
Total means every layer added together. A two-layer 8-inch cake is 2 × 50.3 = 100.6 square inches of pan, and that is the figure to scale from, not 50.3.
Round: area = π × (diameter ÷ 2)²
Square: area = side²
Rectangular: area = length × width
Common pan areas
| Pan | Area |
|---|---|
| 6-inch round | 28.3 sq in (183 sq cm) |
| 8-inch round | 50.3 sq in (324 sq cm) |
| 9-inch round | 63.6 sq in (410 sq cm) |
| 10-inch round | 78.5 sq in (507 sq cm) |
| 12-inch round | 113.1 sq in (730 sq cm) |
| 8-inch square | 64 sq in (413 sq cm) |
| 9-inch square | 81 sq in (523 sq cm) |
| 9×13 rectangular | 117 sq in (755 sq cm) |
A 9-inch square holds about 27% more batter than a 9-inch round. Same number on the label, quite different pan, and it catches people out constantly.
Worked example
A recipe written for two 8-inch rounds, going into three 9-inch rounds.
Original: two 8-inch rounds, 100.5 sq in of pan New: three 9-inch rounds, 190.9 sq in of pan Scale factor = 190.9 ÷ 100.5 = 1.90
So 2.5 cups of flour becomes 4.75 cups, and 3 eggs becomes 5.7. That last one is the awkward part.
Eggs
A large egg is about 50 g out of the shell. When the math lands on 5.7 eggs, crack six, beat them together, and weigh out 285 g. Nobody will ever know. Rounding up to six whole eggs instead adds roughly 5% more egg than the recipe wants, which a sturdy butter cake shrugs off and a delicate sponge does not.
Bake time and temperature
Scaling keeps the batter at its intended depth, so the time moves less than people expect. It does still move. A wider cake takes longer than a narrow one even at the same depth: an 8-inch round runs 30 to 35 minutes at 350°F where a 12-inch runs 35 to 40 at 325°F. Once you are past 12 inches, drop the oven 25°F and give it longer, or the edge browns hard while the middle is still wet.
Capacity
Fill any cake pan between half and two-thirds. If the scaled batter would go past that, split it across another pan or bake the excess as cupcakes. Crowding the pan costs you the rise.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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