It's an argument as old as time, well as old as Italy, anyway. Just how big a pizza should you order to get the best deal?

The small one? The medium one? The one as big as your house? Well, today I'll show you. It's the "yeast" I can do.

Here are five things to know:

  1. Unless you're ordering one of those fancy artisanal pizzas, most are round—basically, a circle. And every circle has something in common. It's pie! This kind of PI. The mathematical number 3.14, which explains the number of times the diameter — the straight line that passes from side to side through the center of the circle — can wrap itself around the edge. That magic number is always the same, 3.14 times (it's a longer number than that, but let's just stick with this for now).
  2. So you want to figure out which pizza is the best value? Which means how much it costs per square inch? Well, here's a formula you need to know: PI R squared. The R is the radius — the length of a straight line from the circle's center to the edge — which is also half the diameter—got that?
  3. Say you have three pizzas: a 6-inch small at $5, a 12-inch medium at $10 and a monster-size 14-inch at $12 bucks. Which is the best value? Let's slice 'em up.
  4. The personal is $5 and only 6 inches in diameter, so the radius is half that at 3 inches. PI 3.14 x 3 inches, squared = 28.26 and $5 divided by 28.26 = 17 cents per square inch of pizza. Bound to be the cheapest, as it's only $5, right?
  5. Using our equation, we find: The medium 12-inch costs $10 and, therefore, is around 9 cents per square inch. And the monster-sized 14-inch is $12, which equals about 8 cents per square inch. So now you can say "good pie" to the personal pizza because the monster-sized one is the way to go in terms of value!

So the next time you and your pals get into it over pizza, just remember the formula: PI R squared. Because, if you don't and you order the more expensive small pizza, your pals might think you are some kind of "weird-dough."