Perimeter of a circle formula

Learn the formula for finding the perimeter of a circle. The term Perimeter is also called as circumference in case of a circle. We have two formulas for perimeter of a circle. One formula will be in terms of radius and another will be in terms of diameter of a circle. So any one formula we can use to find perimeter, but that depends upon the data given in the problem.  

Perimeter of a circle formula

Perimeter (circumference) means the total length of boundary of any geometrical figure. Suppose if the geometrical figure is a polygon then to find the perimeter (circumference) we should add the lengths of all the sides. But circle is not a polygon then what we have to do for finding perimeter (circumference) of a circle. For that we have a formula. Now let us learn that formula

Formula for perimeter (circumference) of a circle:

Let us consider a circle with radius as “r” and centre as “o”.

Perimeter of a circle formula

Perimeter of a circle is given by the formula 2 x π x r where “r” is the radius of the circle and π value we can take \frac { 22 }{ 7 } . The formula is also written as πd since two times of radius is nothing but diameter. Remember the two formulas so that based on problem the right formula we can use.

Perimeter of a circle formula


What is the perimeter of a circle if radius is 21 cm?



                          Radius = 21 cm

We know that

Perimeter or circumference   

 = 2 x π x r

= 2 x \frac { 22 }{ 7 } x 21

= 2 x 22 x 3

= 132 cm

Find the radius of a circle if its perimeter (circumference) is 256 cm.



Perimeter or circumference = 256 cm

2 x π x r       = 256

             r    = 256 x \frac { 7 }{ 22 } x \frac { 1 }{ 2 }

            r    = \frac { 1792 }{ 44 }

           r    = 40.7 cm

I hope you understood the perimeter of a circle formula.

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