Learn these interesting facts about pi before Pi Day on March 14 Facts about pi you don’t want to miss How much do you really know about pi? Sure, you’ve heard about it in math class—potentially sharing a pi joke or two— but this famous number has a history so fascinating that it even has its own holiday.

Pi, which is the ratio of a circle's circumference to its diameter, is celebrated with its own holiday on March 14.

WEST PALM BEACH, Fla. (AP) — Math enthusiasts around the world, from college students to rocket scientists, celebrate Pi Day, which is March 14 or 3/14 — the first three digits of an infinite number with many practical uses. Many people will mark the day with a slice of pie — sweet, savory or even pizza.