Should have a price option to calculate value.

If anyone is confused, this is because area is the square of radius (and Pi, but that factors out when comparing)

So a pizza twice as wide is 4 times as much food.

Doing the math, that means a 10 inch pizza is more than two 7 inch pizzas for example (and that scales, so 20 and 14*2, etc. A really close example is that a 17 inch pizza is just barely more than two 12s. Of course the same thing would work in centimeters, but with bigger numbers or smaller pies)