# Pi

Pi is the mathematical constant defined as the ratio of the circumference of a circle to its diameter with value of approximately 3.14159.

Pi is a middle school-level concept. It is listed in the California State Standards for Grade 6.

### Prerequisites

Circle: | A circle is the set of points in a plane that are equidistant from a given center point. |

Diameter: | (1) In plane geometry, the diameter is the straight-line distance between two points opposite one another across the center of a circle. (2) In solid geometry, the diameter is the straight-line distance between two antipodal points on a sphere. |

Radius: | The radius of a circle is the distance from its center to its circumference or from the center of a sphere to its surface. The radius is equal to half the diameter. |