When Is Pie Day In 2024. Math enthusiasts around the world, from college kids to rocket scientists, celebrate pi day on thursday, which is march 14 or 3/14 — the first three digits of an infinite number. Pi (greek letter “ π ”) is the symbol used in mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3.14159.

March 14, national pi day, honors 3.14 (π) the ratio of the circumference of a circle. Pi day is celebrated on march 14th (3/14) around the world.