Circumference is the distance around a circle. That is, the circumference would be the length of the circle if it were opened up and straightened out to a line segment.
Radius is the distance from the center to the circumference of a circle.
Formula to calculate circumference of a circle:
![How To Calculate Circumference from Radius.](https://www.learntocalculate.com/wp-content/uploads/2020/04/How-to-calculate-circumference-from-radius-2.png)
Where, r is the radius of the circle
and π is a constant estimated to be 3.142 or
![](https://www.learntocalculate.com/wp-content/uploads/2020/03/image.png)
Example:
Calculate the circumference of a circle whose radius is 21 cm. (use π = 3.142)
![How To Calculate Circumference from Radius.](https://www.learntocalculate.com/wp-content/uploads/2020/04/how-to-calculate-circumference-of-a-circle-3.png)
Hence, the circumference of the circle is 131.964 cm.