Sure, as a general rule, you know that it's better to order the larger pizza to get more for your money. If you want to get really mathematical, this calculator will tell you exactly how much more pizza you're getting with a larger size.
This tool, from specialty calculator site Omni Calculator, lets you put in the sizes of two different types of pizzas, the number of each you'd need to order to feed everyone and the cost of each pizza. In response, you'll get both the total area that each option gives you as well as how much each costs. If you've ever been unsure whether to go with fewer larger or more smaller pizzas, this should settle it.
Pizza Comparison [Omni Calculator]