## Introduction

The very common measurements, of a circle, are circumference of circle, area of circle, area of sector, length
of arc and area of segment.

So, let’s discuss them and see how to calculate them.

## Circumference of circle

Circumference is distance around the circle. Its units are the same as that of length i.e meter, centimeter,
millimeter etc.

We can calculate the circumference of circle using the formula as below:

Circumference of circle = 2πr

where, π is a constant value and r is radius of circle

The constant value of π =
$\frac{22}{7}$
or 3.14

**Calculate circumference of circle whose radius is 5cm.**

Here, radius of circle = 5cm

As we know, Circumference of circle = 2πr

∴ Circumference of circle = 2π × 5

= 2 × 3.14 × 5

= 31.4 cm

**What is π?**

π is a value that never changes. If calculated, it always remains constant i.e. 3.14.
**How is it calculated?**

It is calculated by dividing the circumference of the circle to the diameter of the circle.

It is a ratio of circumference and diameter of a circle.

This constant value is denoted by **π** and read as **pi**.

π = $\frac{\mathrm{Circumference}}{\mathrm{Diameter}}$

## Area of circle

Area of circle is a space occupied by a circle. Its units are i.e meter^{2}, centimeter^{2},
millimeter^{2} etc.

Area of circle = πr^{2}

where, π is a constant value and r is radius of circle

Again, the constant value of π =
$\frac{22}{7}$
or 3.14

**Calculate area of circle whose radius is 10cm.**

Here, radius of circle = 10cm

As we know, Area of circle = π^{2}

∴ Area of circle = π × 10^{2}

= 3.14 × 100

= 314 cm^{2}

For the following below measurements, please refer to this figure.

## Area of sector

Area of sector of angle θ =
$\frac{\mathrm{\theta}}{360}$ × π r^{2}

### Area of major sector

Area of major sector OADB = πr^{2} – Area of minor sector OACB

## Length of arc

Length of arc of sector of angle θ = $\frac{\mathrm{\theta}}{360}$ × 2 π r

## Area of segment

Area of segment ACB = π r^{2} – Area of triangle

### Area of major segment

Area of major segment ADB = π r^{2} – Area of minor segment ACB