The greek letter (pi) is a geometric constant that traditionally appears in numerous formulas relating to circles and angles. The value of is naturally occuring and can be found by dividing the length of a circle’s circumference by the length of its diameter.
Shown below are some basic geometric formulas in terms of (pi).
The traditional formula for the area of a circle is given in terms of the geometric constant π (pi).
The volume of a cylinder is equal to PI multiplied by its radius squared and its height.
The constant (pi) traditionally shows up when measuring angles in radians, the preferred unit for measuring angles^{[1]}. Shown to the left below is the circle annotated using (pi). On the right is the circle annotated using (tau) which is the preferred constant for this website.
While (pi) currently appears in advanced formulas through text books and on the web, they are omitted here. See instead the page for (tau) for advanced circle formulas.
The circle constant τ (tau) is a geometric constant approximately equal to 6.283. The numeric value is defined as the length of any circle's circumference divided by the length of its radius.
Radians are a unit that measure angle using the radius of a circle. One radian is equal to the amount of rotation required to travel the length of one radius along the circumference of the circle.

Radians Versus DegreesWumbo (internal)