The distance around a rectangle or a square is as you might
remember called the perimeter. The distance around a circle on the
other hand is called the circumference (c).
A line that is drawn straight through the midpoint of a circle
and that has its end points on the circle border is called the
diameter (d)
Half of the diameter, or the distance from the midpoint to the
circle border, is called the radius of the circle (r).
The circumference of a circle is found using this formula:
Example:
Find the circumference of the circle:
Video lesson: Find the radius of the circle