Planet Money: always buy the bigger pizza because geometry.
The math of why bigger pizzas are such a good deal is simple. A pizza is a circle, and the area of a circle increases with the square of the radius.
So, for example, a 16-inch pizza is actually four times as big as an 8-inch pizza.
And when you look at thousands of pizza prices from around the U.S., you see that you almost always get a much, much better deal when you buy a bigger pizza.