How to adjust pan size in baking

What’s happening to me? The minute I went to photograph this dessert I thought, “Rats! I should have made the cobbler in a cast iron frying pan. It would have looked so much more rustic.”

Great. It’s not enough that I’m criticized for being a food snob. Now I’m about to push myself into a whole new level of visual elitism.

Be warned. Not only can this thought process harm your wallet, it can lead to culinary disaster. Using the correct pan size is crucial in baking. Believe me, I’ve scraped enough batter off the bottom of my oven to know you can’t cram big cake batter into a small cake pan. My only solution was, “Don’t do it.” But with an 8-inch cake stand and loads of recipes for 9-inch cakes, I needed a proper fix.

Fortunately, I surround myself with smart people.

Using Math to Calculate Pan Size

The solution: According to Anna Olson, you need to maintain the depth of the batter to avoid spillage. To do this you need to know:

• the surface area
• the percentage of batter the smaller pan holds

To double check my math, I turned to my cyber-friend Laura Laing, author of Math for Grownups: Relearn the Arithmetic You Forgot from School. (Adams Media © 2011). Ironically, the math I needed wasn’t found in her kitchen section. Instead, I found the required formula in two places. The first — surface area — was illustrated in the gardening section*. Technically, area = pi multiplied by the radius of the circle squared. But I can’t figure out how to type the squared symbol, so I’m going to settle on  A= π x r x r. For easy calculating, I’m rounding pi to 3.14.

First, I need to know the surface area of both pans:

• Surface area for 9-inch round pan = 3.14 x 4.5 x 4.5 = 63.58
• Surface area for 8-inch round pan = 3.14 x 4 x 4 =  50.24

Now I need to now the percentage of the smaller pan. For the ratio formula, I flipped to the section on crafts. Who knew knitting could be so handy? Here’s how much surface area the 8-inch round pan offers versus the 9-inch pan.

• 50.24 / 63.58 x 100 = 79.02%

That’s 80% in my world. In order for the recipe to work, the 8-inch pan should hold only 80% of the batter intended for the 9-inch pan. So, you pour 80% of your batter into the 8- inch pan. (Use a scale to do this.) This ensures the height of the batter is approximately the same as the original recipe intended, and your cake won’t spill over.

And just what do you do with the remaining 20%? Anna says to bake cupcakes. I’d likely just end up eating it by the spoonful.

But wait. There’s more!

This is where math ends and the alchemy begins. Anna says you have to reduce the baking time “slightly”. How much is that? It depends on too many factors to calculate accurately. Reduce the baking time by 5 to 10 minutes, check the cake, and estimate additional cooking time from there  — if needed.

So, will my 10-inch cast iron frying pan work for the cobbler? Let’s see.

• Area of 9-inch square pan = 9 x 9 = 81
• Area of 10-inch round pan = 3.14 x 5 x 5 = 78.5
• Percentage of batter the 10-inch pan will hold = 78.5 / 81 x 100 = 96.9 %

Close enough for me. Think I’ll go make another batch and test the theory in the real world.

Got a tricky kitchen calculation need solving? Ask away. With my calculator and a book of handy formulas, I’m unstoppable.

* For those who are curious about the book, the kitchen section in Math for Grownups help you can calculate how many tomatoes will fit in a jar, convert common measurements, estimate how long it takes to defrost a turkey (and then cook it!) and allow you to fiddle with measuring spoon fractions.