Area grows with the square of the diameter, but menus price sizes as if it grew in a straight line. Test your eye on a few menus, then check your own.
Pick one. The answer is just geometry: area = pi x radius x radius.
Add every option you are choosing between. Round, square or rectangular trays all work.
Every extra inch of diameter adds more than the one before it. Pick a base size and see what each step up gets you.
Area is calculated for a flat circle. Real pizzas have a thicker or thinner crust edge, so use the skip crust field above if you only care about the topped part.