# Formula for Circumference of Circle (Perimeter) – Examples

Here you will learn what is the formula for circumference of circle (perimeter of circle) with examples.

Let’s begin –

## What is Circumference ?

The perimeter (boundary) of a circle is called its circumference. It is the distance covered by travelling once around circle.

## Formula for Circumference of Circle (Perimeter of Circle)

Circumference of circle = $$2\pi r$$

where r is the radius of circle. And $$\pi$$ is an irrational number whose approximate value is $$22\over 7$$ or 3.1415….. unless specified, the value of $$\pi$$ should be taken as $$22\over 7$$

## Circumference (Perimeter) of Semicircle

Perimeter of Semicircle = $$\pi r$$ + 2r = $$r(\pi + 2)$$

#### Rotating Wheels

(i) Distance moved by a wheel in 1 rotation = circumference of the wheel

(ii) Number of rotations in 1 minute = distance moved in 1 minute/circumference.

Example : Find the circumference of the wheel of cycle’s whose diameter is 21 cm.

Solution : We have, Diameter = 21 cm

$$\implies$$   Radius = $$21\over 2$$  = 10.5 cm

Circumference = $$2\pi r$$  = $$2 \times {22\over 7} \times 10.5$$ = 66 cm

Hence, the circumference of wheel of cycle is 66 cm

Example : If the diameter of a semi-circular plot is 14 m, then find its perimeter.

Solution : A semi-circle has been drawn with AB = 14 m as diameter.

$$\therefore$$  Its radius,     r = $$d\over 2$$ = $$14\over 2$$ = 7 m

$$\therefore$$   Perimeter of semi-circle of radius 7 m = $$\pi r$$ + 2r  = $${22\over 7} \times 7$$ + $$2\times 7$$ = 36 m

Hence, the required perimeter is 36 m.