Cake Pan Size Conversion: Chart, Formula, and 9x13 to 8x8
To convert a recipe from one cake pan to another, compare the pans by area, not by their width. Divide the area of the pan you are baking in by the area of the pan the recipe was written for, and multiply every ingredient by that number. A 9x13 pan is 117 sq in; an 8x8 is 64 sq in. So a 9x13 recipe in an 8x8 needs 0.55 times the ingredients - about 55% of the batch. Going the other way, an 8x8 recipe in a 9x13 needs 1.83 times as much.
The formula
- Rectangle or square: area = width x length
- Round: area = 3.1416 x radius x radius (the radius is half the diameter)
- Scaling factor: factor = area of new pan / area of recipe’s pan
- New amount of each ingredient: old amount x factor
This keeps the batter at the same depth in the new pan, which is what keeps the bake behaving like the original. Use the same unit for both pans.
Cake pan size conversion chart
Pan sizes below are nominal - the size the pan is sold as. Real pans have sloped sides and rounded corners, and some are measured across the rim rather than the base, so measure yours across the inside bottom if the result matters.
| Pan (nominal) | Area | Same area as a square of side |
|---|---|---|
| 8 x 8 in square | 64 sq in | 8.00 in |
| 9 x 9 in square | 81 sq in | 9.00 in |
| 9 x 13 in rectangle | 117 sq in | 10.82 in |
| 8 in round | 50.27 sq in | 7.09 in |
| 9 in round | 63.62 sq in | 7.98 in |
| 10 in round | 78.54 sq in | 8.86 in |
| 8.5 x 4.5 in loaf | 38.25 sq in | 6.18 in |
| 9 x 5 in loaf | 45 sq in | 6.71 in |
The last column turns every pan into a square of the same area. It is the quickest way to see which pans are interchangeable: a 9 in round is 63.62 sq in and an 8x8 square is 64 sq in, so a 9 in round recipe baked in an 8x8 needs a factor of 1.01 - no real scaling at all.
Pan-to-pan conversion factors
Find the pan your recipe was written for in the left column, then read across to the pan you are baking in. Multiply every ingredient by that number.
| Recipe for \ Baking in | 8x8 | 9x9 | 9x13 | 8 rd | 9 rd | 10 rd |
|---|---|---|---|---|---|---|
| 8x8 | 1.00 | 1.27 | 1.83 | 0.79 | 0.99 | 1.23 |
| 9x9 | 0.79 | 1.00 | 1.44 | 0.62 | 0.79 | 0.97 |
| 9x13 | 0.55 | 0.69 | 1.00 | 0.43 | 0.54 | 0.67 |
| 8 rd | 1.27 | 1.61 | 2.33 | 1.00 | 1.27 | 1.56 |
| 9 rd | 1.01 | 1.27 | 1.84 | 0.79 | 1.00 | 1.23 |
| 10 rd | 0.81 | 1.03 | 1.49 | 0.64 | 0.81 | 1.00 |
Loaf pans work the same way: an 8.5 x 4.5 recipe baked in a 9 x 5 loaf pan needs 1.18 times the batter.
Worked example: 9x13 to 8x8
An illustrative recipe written for a 9x13 pan, scaled by 0.547 for an 8x8:
| Ingredient | 9x13 recipe | x 0.547 for an 8x8 |
|---|---|---|
| Flour | 3 cups | 1.64 cups |
| Sugar | 2 cups | 1.09 cups |
| Milk | 1 cup | 0.55 cup |
| Butter | 1 cup | 0.55 cup |
| Eggs | 4 | 2.19 |
Two practical points come out of the table:
- Eggs do not divide neatly. 2.19 eggs is not something you can crack. Beat all the eggs you would need for a round number together, weigh the bowl, and use that fraction of the weight. Rounding to a whole egg is the other option, and it changes the recipe by a fraction of an egg.
- Halving is close but not exact. Half a 9x13 recipe in an 8x8 gives a layer 91% as deep as the original - about 9% thinner. For a brownie that is a small change; if you want the original thickness, use the 0.547 factor instead of 0.5.
If you skip the scaling and pour the whole 9x13 batch into an 8x8, the batter is 1.83 times as deep. That is a different bake, and the pan may not be tall enough to hold it.
Worked example: 8 in round to 10 in round
A 10 in round is only 25% wider than an 8 in round, but its area is 78.54 sq in against 50.27 sq in - 56% more batter.
| Ingredient | 8 in round recipe | x 1.562 for a 10 in round |
|---|---|---|
| Flour | 2 cups | 3.12 cups |
| Sugar | 1.5 cups | 2.34 cups |
| Eggs | 3 | 4.69 |
This is the non-obvious part of pan conversion: area grows with the square of the diameter, so a small step up in pan size is a large step up in batter. Scaling by the diameter (x 1.25 here instead of x 1.56) would leave the cake noticeably thin.
The same rule explains why a round and a square of the same nominal size are not the same pan. An 8 in round has 79% of the area of an 8x8 square, because the round leaves out the corners.
Splitting a 9x13 into layers
A 9x13 recipe is sometimes baked as two round layers instead. The numbers:
- Two 9 in rounds total 127.23 sq in, which is 1.09 times the 9x13. The batter fits, at 92% of the original depth - slightly thinner layers.
- Two 8 in rounds total 100.53 sq in, only 0.86 times the 9x13. The full batch would sit at 116% of the original depth. Check that your pans are tall enough, or hold some batter back for cupcakes.
What about baking time?
Area scaling keeps the batter depth the same, and depth has a large effect on how long the center takes to set. When the depth matches, the original time is a starting point to check against, not a promise: a pan with a different shape, material or color can still bake faster or slower. Area alone does not give you a bake time, so this page does not offer a time formula.
What to do instead:
- Start checking early. Look at the cake well before the original time is up, then keep checking. Use the doneness test the recipe gives - a toothpick in the center, the top springing back, the edges pulling away.
- Expect longer if the batter is deeper. If you have poured more batter than the factor says (the whole 9x13 batch into an 8x8, say), the center will take longer to set and the edges can overbake while it does. Check the pan’s height before you fill it.
- Expect shorter if the batter is thinner. Halving a 9x13 into an 8x8 gives a slightly thinner layer, so test earlier.
How these were calculated
Every area, factor and table cell on this page is computed in code and checked two ways before the page builds. Round pan areas come from the formula (pi x radius squared) and, separately, from adding up thin strips across the circle with no use of pi; rectangles come from width x length. The round-pan and rectangular-pan tables printed on the wall chart below were also recomputed and had to match. Factors are the new area divided by the old area. Pan sizes are nominal, and the recipes in the worked examples are illustrative, not tested recipes. This is arithmetic, not baking advice: watch the cake, not the clock.
If you would like the scaling factors on the wall - round pans from 6 to 12 inches, plus 8x8, 9x9, 9x13 and two loaf pans - along with oven temperature and measure conversions, this one-page chart prints them: