March 14 is Pi Day!! Pi Day is celebrated on March 14th (3/14) around the world. 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. ... Pi has been calculated to over one trillion digits beyond its decimal point. Have fun with 3.14 by using 3 colors in 14 minutes to color in the boxes.