When ordering pizza for guests (or when throwing yourself a personal pizza party), it can be tempting to spring for two medium pies over one large one. It may end up being more expensive, but it also feels like the logical choice: Two 12-inch pies should give you more cheesy goodness per square inch than an 18-inch pie, right?

That may be what pizzerias want you to think, but as Fermat's Library recently illustrated on Twitter, it's not the case. One large, 18-inch pie boasts a full 28 more square inches of pizza than two small 12-inch pies, making the larger pie by far the better deal.

Even though the diameter of the large pizza is smaller than the combined diameters of the two medium pies, it still has a larger total area. To get the area of the circle, you have to square the radius (which is half of the diameter) and multiply that by pi (about 3.14). This means the area of an 18-inch pizza is 254 square inches, while the combined area of two 12-inch pies is only 226 inches.

The geometry required to calculate your pizza order isn't too complicated, but the tweet was apparently eye-opening enough to garner a viral response. Some people were thankful for the math tip, while others had trouble wrapping their heads around it. Mathematician Tamás Görbe pointed out that while an 18-inch pie technically gives you more food, two 12-inches pies give you 33.3 percent more crust—something to keep in mind if that's your favorite part.

In case you're looking for another excuse to order pizza, January 13 marked the start of National Pizza Week. Here are some facts about the beloved dish to celebrate the occasion.

[h/t Mashable]