Wrong pan? Right math.
The recipe wants a 9 inch round and you own an 8 inch square. Pick both pans and get the exact scaling factor.
To swap cake pans, match the AREA, not the diameter. An 8 inch round holds 50 sq in, a 9 inch round 64 sq in, so a 9 inch pan needs about 1.3 times the batter. Same batter in a wider pan means a thinner cake, so cut 5 to 10 minutes off the bake time and start checking early.
Cake pan size chart
Divide the target pan's area by your recipe's pan area to get the batter multiplier.
| Pan | Area | vs 8 inch round |
|---|---|---|
| 6 inch (15 cm) round | 28 sq in | 0.56x batter |
| 8 inch (20 cm) round | 50 sq in | 1x batter |
| 9 inch (23 cm) round | 64 sq in | 1.28x batter |
| 10 inch (25 cm) round | 79 sq in | 1.58x batter |
| 8 inch (20 cm) square | 64 sq in | 1.28x batter |
| 9 inch (23 cm) square | 81 sq in | 1.62x batter |
| 9 x 13 inch (23 x 33 cm) rectangle | 117 sq in | 2.34x batter |
| 10 x 15 inch (25 x 38 cm) jelly roll | 150 sq in | 3x batter |
| 9 x 5 inch (23 x 13 cm) loaf | 45 sq in | 0.9x batter |
| 8.5 x 4.5 inch (21 x 11 cm) loaf | 38 sq in | 0.76x batter |
| 9 inch (23 cm) springform | 64 sq in | 1.28x batter |
| 10 inch (25 cm) springform | 79 sq in | 1.58x batter |
| 10 inch (25 cm) bundt | 72 sq in | 1.44x batter |
| 12-cup muffin tin | 53 sq in | 1.06x batter |
Depth matters too: these assume the standard 2 inch (5 cm) pan depth. Never fill a pan more than two thirds.
Pan sizes are the silent cake killer: the same batter is 3 cm deep in one pan and 5 cm in another, and the bake time swings by 20 minutes. This converter compares the surface area of 14 common pans and tells you how to scale the recipe.
Questions people ask
Can I use a 9 inch pan instead of an 8 inch?
Yes, with two adjustments. A 9 inch round is about 1.3 times the area of an 8 inch, so the same batter bakes thinner and faster. Reduce the temperature slightly or just start checking 5 to 10 minutes before the recipe says.
How do I convert a round pan to a square pan?
By area. An 8 inch square is 64 sq in, the same as a 9 inch round, so those two swap 1:1. A 9 inch square (81 sq in) needs about 1.3 times the batter of a 9 inch round.
Do I need to change the baking time when I change pan size?
Almost always. Batter depth drives bake time far more than pan diameter does. A thinner layer sets faster: check for a clean skewer at about 75 percent of the original time.
How full should a cake pan be?
About two thirds, never more. Cake batter climbs as the leavening works, and a pan filled to the brim either domes and cracks or spills over the side.
Good to know
That is the range cake batter wants. Fuller than two-thirds risks overflow and a sunken center, emptier than half bakes into a sad pancake with dry edges.
If your pan makes the batter noticeably deeper than the original, drop the oven about 15 C / 25 F and expect extra minutes. Shallower batter bakes faster, so start checking early.
Whatever the math says, a skewer in the center coming out with a few moist crumbs is the real done signal. Converted pans are exactly when you trust the tester over the clock.
Cooking guides
Recipes in the Pann app scale their quantities automatically when you change servings, and Cook Mode adjusts the steps to match.