MathMaster Blog

The circumference of a circle (or any circular shape) is the distance around it. The circumference of a circle equals the length of a straight line folded or twisted to form the circle. There are two ways of finding the perimeter or circumference of a circle.

#1: When the radius is known:

where

C = Circumference or perimeter,

R = the radius of a circle

π = 3.14.

#2: When the diameter is given:

where D = 2R = The diameter of a circle.

For any circle, its circumference ratio to its diameter is equal to a constant known as pi.

Example 1:

Calculate the circumference and area of a 14-cm-radius circle.

Solution:

Circumference of the circle = 2πr

= 2 x 22/7 x 14

= 2x 22 x 2

= 88 cm

Using area of Circle formula πr^2:

= 22/7 x 14 x 14

= 22 x 2 x 14

= 616 sq.cm.

Answer: The area of the circle is 616 sq.cm.

Example 2:

Calculate the circumference of a 70-mm-diameter circle.

Solution:

Circumference = π*D = πD = 3.14 * 70 = 219.8 mm

Answer: 219.8 mm.

Example 3:

A wheel's circumference is 440 cm. Calculate its radius and diameter.

Solution:

440 = 2r

440 = 2 x (22/7) x r

Radius = 70 cm

Diameter = 2 x radius

Diameter = 2 x 70

Answer: The radius is 70 cm, and the diameter is 140 cm.