We know that circle is a closed figure which is the path described by the point which moves such that it is at a constant distance from a fixed point. We are already aware of the parts of a circle, which is the center, radius, diameter, chord and the properties of chords of a circle. Being a two dimensional we can find the area and circumference of a circle. We are familiar in finding the perimeter of a square or a rectangle, which is the sum of all the sides, which is the boundary of a closed figure. When we increase the number sides of a regular polygon, the perimeter or the length of the boundary is the sum of all the sides, called the perimeter of the closed figure. In this section let us see how to find the circumference of a circle.

What is circumference? It is the length of the boundary of a circle. It is the length of the arc of the closed curve. It is also called the perimeter of the circle.

Let us observe the following circles.
Circumference Definition
In the above figure, we observe that the length of the boundary of the circle increases as the radius increases.
Therefore, the boundary of the circle depends on the radius of the circle.

Circumference of a Circle Formula

We know that diameter of a circle d = 2 x radius = 2 r
The circumference is calculated using the formula C = 
2 $\pi$ r