Pi (π) is the mathematical symbol for the constant that equals the ratio of a circle’s circumference to its diameter, approximately 3.14159.

What the symbol π means

  • π is a constant number: for every circle, big or small, circumference ÷ diameter is always π.
  • Its value is about 3.14 in everyday use, but its decimal expansion never ends and never repeats (it is an irrational number).
  • In formulas, π shows up whenever circles, rotations, or waves are involved, for example in the circumference formula C=2πrC=2\pi rC=2πr and area formula A=πr2A=\pi r^{2}A=πr2.

A bit of background

  • The symbol π is the Greek letter “pi,” chosen because it is the first letter of the Greek word related to “periphery” or “circumference.”
  • It was first used for this ratio in the early 1700s by William Jones and later made standard by the mathematician Leonhard Euler.

Beyond circles

  • π also appears throughout physics and engineering, for example in formulas involving waves, oscillations, and probability distributions.
  • Because of its mysterious, never‑ending digits and its connection to circles, π has become a popular cultural icon, celebrated every year on “Pi Day” (March 14, i.e., 3/14).

Information gathered from public forums or data available on the internet and portrayed here.