How this calculator works
Batter depth stays about the same when the scaling factor equals the ratio of pan areas. The calculator computes the area of each pan (π r² for round, side² for square, length × width for rectangles), multiplies by the number of pans and divides.
Round area = π × (Diameter ÷ 2)²
Square area = Side²
Rect area = Length × Width
Factor = Your pans’ total area ÷ Recipe pans’ total area
Assumptions and tips
- Assumes both pans have similar depth. Bundt and tube pans need volume, not area.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Recipe’s pan shape | Round |
| Diameter / side / length | 9 in |
| Number of pans in recipe | 2 |
| Your pan shape | Rectangle |
| Diameter / side / length | 13 in |
| Width | 9 in |
| Number of your pans | 1 |
| Result | Value |
|---|---|
| Multiply the recipe by | 0.92 × |
| Recipe pan area (total) | 127.2 sq in |
| Your pan area (total) | 117 sq in |
Step by step:
- Recipe pans = 127.23 sq in
- Your pans = 117 sq in
- Factor = 117 ÷ 127.23 = 0.92
Pan areas
Compared with one 9 in round pan.
| Pan | Area | vs. one 9 in round |
|---|---|---|
| 8 in round | 50.3 sq in | 0.79 × |
| 10 in round | 78.5 sq in | 1.23 × |
| 8 in square | 64 sq in | 1.01 × |
| 9 in square | 81 sq in | 1.27 × |
| 9 × 13 in | 117 sq in | 1.84 × |
| 11 × 17 in sheet | 187 sq in | 2.94 × |
Common mistakes to avoid
- Filling a pan more than about two-thirds full.
Frequently asked questions
Can I bake two 9-inch rounds in a 9×13?
Yes — two 9 in rounds total about 127 sq in, close to a 9×13 at 117 sq in, so the recipe fits with a slightly thicker layer.
How do I adjust baking time?
Keep the temperature, and start checking at the original time; deeper or larger cakes usually need longer.