Pi

The mathematical constant pi (π) is defined as the ratio of a circle's circumference to its diameter. It is also the ratio between a circle's area and its radius squared. It is approximately equal to 3.14159, but has been calculated to over one trillion digits.^{1 2}

Fast Facts

1. First approximated by Babylonians earlier than 1680 BC³
2. Measured by Babylonians to be 3.125³
3. William Jones first used the pi symbol (π) in 1706¹
4. The use of the symbol was adopted by mathematician Leonhard Euler in 1737¹
5. Current calculations extend it to over one trillion digits¹
6. Pi Day is celebrated in the United States on March 14¹
7. 22/7 is often used as an approximation for pi⁴
8. 355/113 is a closer approximation of pi⁴

History

Pi was approximated by the Babylonians over 4000 years ago. They measured it to be 3.125 according to a tablet dating back to approximately 1700 BC. An Egyptian papyrus document, dating back to 1650 BC, shows that the Egyptians used 3.1605 as the constant to calculate the area of circles. Ancient mathematician Archimedes calculated pi by using the Pythagorean Theorem. He judged it to be between 3 1/7 and 3 10/71.³

Despite the long available knowledge of the constant, a universal symbol was not used to describe it until the 1700s. William Jones was the first to use the symbol "π" in 1706. Leonhard Euler began using the symbol in 1737 after which it became popularized.³

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