The perimeter or circumference of a circle is given by the formula: Circumference = 2*pi*r , where r is the radius of the circle and pi is a constant.

If you know the radius of the circle, just substitute r in the formula given and you have the circumference or perimeter of the circle.

**The perimeter of a circle with radius r is given by 2*pi*r.**

The perimeter of a circle with radius r is given

by Pi *r*r ...(1)

The problem is that the exact value of Pi is unknown and hence it is impossible to determine the value of the perimeter.

However, if you agree to approximate the value of pi (usually taken as 22/7 OR 3.14159), the approximate value of the perimeter may be calculated by using (1).