Happy Pi Day! Pi Day is definitely one of my favorite holidays, right up there with Halloween and 4th of July. But, what is Pi day? Pi day is celebrated on March 14, which can be shortened to 3-14 which is very similar to 3.14, the rounded off number for pi. Ta da! Pi day! Sometimes abbreviated with the Greek letter, π, pi is mathematically equivalent to the ratio of the circumference of a circle divided by the diameter. It has been calculated to over a trillion places beyond the decimal point, and doesn’t have a pattern. While the human body doesn’t have any mathematically exact ratios like pi, it does have some other interesting, approximate ratios, both internally and externally.