Pi Day celebrates the pi symbol (π) and its importance to mathematics. The symbol is a Greek letter, and it is used in mathematics to represent the ratio of the circumference of a circle to its diameter. The first digits of this ratio are 3.14159, and the number continues infinitely without pattern. It has been calculated to over one trillion digits after the decimal point. Most calculations only need the first few digits. Even the spherical volume of the whole universe can be calculated by using just 39 digits after the decimal point. The symbol "π" was first used in 1706 by William Jones. It gained in popularity after being used by Swiss mathematician Leonhard Euler in 1737. The first large and official celebration of the day took place at the San Francisco Exploratorium in 1988. It was organized by Larry Shaw, a physicist at the Exploratorium. At the inaugural event, people marched around a circular space and ate fruit pies. In 2009, the U.S. House of Representatives passed a resolution supporting Pi Day.

Pi Day is observed next on Saturday, March 14th, 2020. It has been observed annually on March 14th since 1988.

How to Observe

Pi Day can be celebrated in a few ways:

Occurrence Patterns

ObservedFirst YearLast Year
annually on March 14th1988-




  • Founded by Larry Shaw in 1988


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