Pi = $3.14

Pi Day, a global celebration of all things round (like pizza), is nearly here. That means it’s time for our annual special: order one 11” pizza, and get a second 11” pizza for just $3.14.

How many square inches of pizza is that?

Here’s the math:

πr²

2 × (π × 5.5²) = 190 square inches

All for $3.14 (with your favorite toppings!).

Without pi, an irrational and transcendental marvel, we couldn’t even calculate the area of a pizza. We started our annual Pi Day celebration in Seattle in 2014. A year earlier, Pagliacci co-owner Matt Galvin delivered several pizzas to his son’s math class for Pi Day. The thank-you cards that came back suggested a $3.14 pizza special. We liked the math. Twelve years later, it’s still going strong.

Though Pi Day is often treated like a culinary holiday, the celebration itself is relatively new. It began in 1988 at San Francisco’s Exploratorium, thanks to physicist Larry Shaw, fondly dubbed the “Prince of Pi.” Shaw placed a small brass marker called “The Interdimensional Rotator,” ringed by the first 100 digits of pi, and invited visitors to circle it three and one-seventh times while chanting pi’s digits and singing “Happy Birthday” to Einstein (whose birthday is March 14). That playful ritual caught on and then went global. Shaw once joked that “ours is a mystery religion,” noting that, like other traditions, we circle the things we respect.

Pi is the ratio of a circle’s circumference to its diameter: about 3.14, though its decimals run on to infinity. The ratio has been around since ancient times, but it was Archimedes, some 2,300 years ago, who first showed how to estimate the value of pi with precision—by harnessing infinity. His method was beautifully practical: approximate a curved circle with many tiny straight edges, then keep adding more sides until the shape becomes nearly indistinguishable from the curve. Pi never ends and never repeats, but it keeps showing up everywhere we try to measure the world of curves.

Whether you love math or love to hate it, raise a slice to the circular wonder of pizza this Pi Day. Our special offer — buy one 11” pizza, get a second 11” pizza for $3.14 — is available for delivery, pick-up, or dine-in customers on March 14. (Other offers can’t be combined.)