Lafayette pie shop celebrates Pi Day and last updated 2021-03-13 23:16:55-05 Sunday, March 14, is a special day for math (and pie) lovers - it's National Pi Day! Pi Day dates back to 1988, when physicist Larry Shaw with the Exploratorium in San Francisco realized that the date 3/14 echoes the first three digits of pi, a constant value used in math to represent the ratio of the circumference of a circle to its diameter. Shaw invited employees for pie and tea on 3/14 at precisely 1:59 pm. The first five numbers of pi are 3.14159, and pies are typically round, like a circle, so Shaw's precise timing and choice of dessert were no accidents â and Pi Day was born. On March 12, 2009, the U.S. Congress ensured the holiday's success when they recognized 3/14 as National Pi Day.