#### What is circumference anyway?

**Answer:** The circumference of a circle is the edge or rim of a circle itself. It is the equivalent of 'perimeter' for a circle. In other words, if you took a circle and unrolled it, you would have its circumference. You can use either of the formulas below to find the circumference . One formula use the radius of a circle; the other formula uses the diameter.

#### What is the formula for circumference?

**Answer:**

Formula using Diameter |
Formula using Radius |

$$ Circumference = \pi \cdot diameter $$ |
$$ Circumference = 2\pi\cdot radius $$ |

**These two formulas are just two different ways of finding the same thing (circumference) because the diameter of a circle =2• radius. So you can use whichever formula is more convenient. If you know a circle's radius, use the first version of the formula; if you know the diameter, use the second

### The Circle Song

The rotating line on the left is an example of a circle's radius.

If the radius of a circle is 1 inch (1"), then the **circumference** of the circle = 2 Π • 1" ≈ 6.28 "