Illustration of pizza.

It’s a weeknight, the kids are hungry, work ran late and the fridge is empty. The only question: What size pizza are you ordering?

James Baglama, chair of URI’s Mathematics Department, can help. His local is Kingston Pizza, where a small 10-inch pie with one topping rings in at roughly $7, while the Big City 18-incher costs $16.

“It seems two 10-inch pizzas, with a total cost of $14, is giving you more pizza for less money than the 18-inch pizza,” Baglama observes. “But is it?”

Assuming uniform thickness and setting aside the thorny issue of topping choice, Baglama walks us through the math. “The formula for the surface area is (π/4) x D2, where D represents the diameter,” he says. “A 10-inch pizza has a surface area of (π/4) x 102—about 79 square inches. An 18-inch pizza has a surface area of (π/4) x 182—about 254 square inches. So, two 10-inch pizzas (79 +79) give you about 158 square inches of pizza, while the 18-inch pizza gives you 254 square inches.”

Follow that? Here’s the take-away: There is more surface area in one 18-inch pizza than in three 10-inch pizzas. So go ahead: order the large!