Pi is the ratio of the circumference of a circle to its diameter. It's rounded up because the actual ratio has been calculated to over one trillion digits beyond the decimal point (which sounds like fun to read while swiping on a phone). The symbol for Pi (π) was first used in 1737 by Swiss mathematician Leonhard Euler.

The diameter of a circle is the distance from edge to edge, measuring straight through the center. The circumference of a circle is the distance around.
By measuring circular objects, it has always turned out that a circle is a little more than 3 times its width around. In the Old Testament of the Bible (1 Kings 7:23), a circular pool is referred to as being 30 cubits around, and 10 cubits across. The mathematician Archimedes used polygons with many sides to approximate circles and determined that Pi was approximately 22/7. The symbol (Greek letter “π”) was first used in 1706 by William Jones. A ‘p’ was chosen for ‘perimeter’ of circles, and the use of π became popular after it was adopted by the Swiss mathematician Leonhard Euler in 1737. In recent years, Pi has been calculated to over one trillion digits past its decimal. Only 39 digits past the decimal are needed to accurately calculate the spherical volume of our entire universe, but because of Pi’s infinite & patternless nature, it’s a fun challenge to memorize, and to computationally calculate more and more digits.

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