# Circle: Circumference

How to find the circumference of a circle: 2 formulas, 2 examples, and their solutions.

## Formula

### Formula

C = 2πr

C: Circumference of a circle

r: Radius

If a radius is given,

use this formula.

C = πd

d: Diameter

If a diameter is given,

use this formula.

## Example 1

### Example

### Solution

r = 5

So use C = 2πr.

C = 2π⋅5

2π⋅5 = 10π

So 10π is the answer.

## Example 2

### Example

### Solution

d = 13

So use C = πd.

C = π⋅13

π⋅13 = 13π

So 13π is the answer.