Pi Day, observed annually on March 14, honors the mathematical constant π and its applications. In 2026, International Mathematics Day's theme is 'Mathematics and hope,' emphasizing math's universal role in understanding reality. UNESCO states that mathematics supports shared frameworks and solutions for the common good.
Pi Day falls on March 14 because the first three digits of π, 3.14159, align with the date 3/14. The constant π represents the ratio of a circle's circumference to its diameter and is used to compute areas and volumes of circular and spherical objects. As an irrational number denoted by the Greek letter π, it appears in numerous formulas in mathematics and physics.
The Greek letter π was adopted in 1706 by Welsh mathematician William Jones, derived from Greek words for 'periphery' and 'perimeter.' Over centuries, mathematicians like Archimedes calculated π using various methods. The first Pi Day observance occurred in 1988, organized by American physicist Larry Shaw at the San Francisco Exploratorium. On March 12, 2009, the U.S. House of Representatives passed a resolution recognizing March 14 as National Pi Day. The date also marks the birth anniversary of physicist Albert Einstein.
A common tradition involves eating pie, a homophone for pi, symbolizing the circular shape. March 14 is also International Mathematics Day, proclaimed by UNESCO in November 2019 to highlight math's role in addressing real-world challenges and advancing science and technology.
For 2026, the theme is 'Mathematics and hope.' UNESCO explains that 'mathematics enables a deeper understanding of reality, supports the development of shared frameworks and definitions, and strengthens collaboration across disciplines and societies. Through responsible use of data and rigorous reasoning, mathematics contributes to solutions that serve the common good.' It aids in navigating uncertainty, building trust in knowledge, and fostering inclusive futures, while enhancing social cohesion and resilience.
To commemorate the day, Google released an interactive Doodle featuring Archimedes' method of approximating π by inscribing a circle between two 96-sided polygons. The Doodle notes, 'This Doodle celebrates the numerical constant pi (π), highlighting the foundational geometry first used to calculate its limits.'