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** (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** 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.

**Examples:**

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

Solution:

Given

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.

Solution:

Given

**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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