Math Matters: The Size of the Baking Dish

It’s often said that baking is a science – and that is certainly true – but the equally important skill when baking is math. (Have I mentioned that I was a math major?) Lucky for most of us, the math needed for baking is much simpler than algebraic equations and linear algebra, but basic math (addition, subtraction, multiplication, division) and geometry come in quite handy when baking. I always keep a calculator in the kitchen (the calculator on your phone works too), and a ruler nearby.

Today’s lesson is about the size of a baking dish:

A 10-inch pie plate is considerably larger than a 9-inch plate. That inch might not seem to make much difference, but you need considerably more pie dough and filling to make a 10-inch pie. Check out the math:

Area equals pi (3.14) times the radius squared.

A 9-inch pie plate has an area of 64 inches (4.5 x 4.5 x 3.14) whereas a 10-inch pie plate has an area of 79 inches (5 x 5 x 3.14). That’s a difference of 23%.

Whereas some recipes can be adapted for plate size (for example, a brownie recipe designed for a 9-inch-square pan can be made in an 8-inch-square pan by increasing the baking time, don’t try to use a 10-inch pie plate with a recipe that was designed for a 9-inch pie. You won’t have enough crust and the filling will fall flat.

If you must use a 10-inch pie plate with a recipe designed for a 9-inch pie plate you need to increase the ingredients by roughly one quarter (or 5 parts for every 4 that the recipe calls for).