## Mathematics Throughout History## The Creation of Zero and Pi |

## What are the measurements of a circle using pi? |

There are many measurements of a circle. The perimeter of a circle is called the *circumference;* to calculate, multiply pi (π) times the diameter, or *c =* (πd), or pi (π) times twice the radius, (c = 2πr). The area (a) of a circle is calculated by multiplying pi (π) times the radius squared, or *a* = π*r*^{2}.