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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:

Formula

Circumference of circle = 2πr
where, π is a constant value and r is radius of circle
The constant value of π = 227 or 3.14

Example

Calculate circumference of circle whose radius is 5cm.
Here, radius of circle = 5cm
As we know, Circumference of circle = 2πr
∴ Circumference of circle = 2π X 5
= 2 X 3.14 X 5
= 31.4 cm

Note

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 = CircumferenceDiameter

Area of circle

Area of circle is a space occupied by a circle. Its units are i.e meter2, centimeter2, millimeter2 etc.

Formula

Area of circle = πr2
where, π is a constant value and r is radius of circle
Again, the constant value of π = 227 or 3.14

Example

Calculate area of circle whose radius is 10cm.
Here, radius of circle = 10cm
As we know, Area of circle = π2
∴ Area of circle = π X 102
= 3.14 X 100
= 314 cm2

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

Sector area of circle
Sector area of circle

Area of sector

Formula

Area of sector of angle θ = θ360 X π r2

Area of major sector

Formula

Area of major sector OADB = πr2 – Area of minor sector OACB

Length of arc

Formula

Length of arc of sector of angle θ = θ360 X 2 π r

Area of segment

Formula

Area of segment ACB = π r2 – Area of triangle

Area of major segment

Formula

Area of major segment ADB = π r2 – Area of minor segment ACB