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,

National Pi Day 2025 brings pizza and pie deals nationwide, with discounts like $3.14 pizzas and freebies from major chains.

Friday is Pi Day, a national celebration of the mathematical concept, which is the ratio of a circle's circumference to its diameter and equals 3.14... Schools and museums often plan events to celebrate the concept, which has fascinated humans for centuries, and local eateries offer pie-related deals.