In math, "pi" is equal to?

In math, “pi” is equal to approximately 3.141592654. Pi is the constant ratio of a circle’s circumference to its diameter, so dividing the circumference of any perfect circle by its diameter gives the same number. The stored value is rounded to nine decimal places; the full decimal expansion begins 3.141592653589793 and continues forever.

Pi is irrational, meaning it cannot be written exactly as a fraction of two integers, and it is also transcendental, meaning it is not the solution of any nonzero polynomial equation with rational coefficients. These properties make its digits nonterminating and nonrepeating.

Ancient Babylonian and Egyptian mathematicians used early approximations. Around 250 BC, Archimedes estimated pi with inscribed and circumscribed polygons. The Greek letter π became associated with the constant in 1706 through Welsh mathematician William Jones, although Leonhard Euler later helped popularize the notation.

A common mix-up is treating 22/7 as pi. It is a useful approximation, but slightly larger than the true value. Pi appears in formulas for circles, spheres, waves, trigonometry, physics and engineering.