Pan size conversion

Cake tins scale by area, not by width. A 9-inch round holds about 26 percent more than an 8-inch round, and a 10-inch holds 56 percent more. Pick what the recipe wants and what you actually own, and this works out the multiplier and what it does to the bake time.

×1.26
Multiply every ingredient by this. 26% more batter than the original.
200 g flour
252.9 g
3 eggs
3.8
250 ml milk
316.1 ml

Timing. The batter sits shallower, so it bakes faster. Start checking 5 to 10 minutes early.

About the 9-inch round. Almost exactly the same area as an 8-inch square, which is why the two swap cleanly with no timing change at all.

Common tin sizes

TinMetricAreaHolds
6-inch round15 cm round28.3 in²4 cups
7-inch round18 cm round38.5 in²5.5 cups
8-inch round20 cm round50.3 in²6 cups
9-inch round23 cm round63.6 in²8 cups
10-inch round25 cm round78.5 in²10 cups
8-inch square20 cm square64 in²8 cups
9-inch square23 cm square81 in²10 cups
9x13-inch rectangular23 x 33 cm117 in²14 cups
8.5x4.5-inch loaf21.5 x 11.5 cm38.3 in²6 cups
9x5-inch loaf23 x 13 cm45 in²8 cups
10-inch bundt25 cm bundt78.5 in²12 cups
10-inch tube pan25 cm tube78.5 in²16 cups
9-inch springform23 cm springform63.6 in²10 cups
10-inch springform25 cm springform78.5 in²12 cups
12-cup muffin tin12 wells, 7 cm across70.7 in²6 cups
8-inch pie dish20 cm pie dish50.3 in²4 cups
9-inch pie dish23 cm pie dish63.6 in²5 cups
9-inch deep dish pie23 cm deep pie dish63.6 in²6.5 cups
10x15-inch jelly roll25 x 38 cm150 in²10 cups

Converting the ingredient amounts too? Grams to cups by ingredient, and oven temperatures in fan and gas mark.