How to Find the Circumference of a Circle

Of the various two dimensional geometrical figures, circle is one with no side or end. It is similar to a ring. Circumference to a circle is what perimeter is to a square or a rectangle. In simple language it is the rim of a circle. If we take a string and make a circle out of it, then the entire length of the string would give the circumference of the circle that it formed. Other than being able to solve problems given as homework, there are various practical applications for which we need to know how to find the circumference of a circle.

Different Parts of a Circle
There is a formula which can be used to calculate circumference of a circle. It involves various aspects of a circle. Hence before using the equation, one should be conversant of the various parts/aspects of a circle like:

The Center: It is the exact point inside a circle such that all points on the circle are equidistant from it. Each circle has just one center.

Radius (r): Radius is the shortest distance of the center from any point on the circle.

Diameter (d): It is a straight line that starts and ends in two points on the circle and also passes through the center. Hence as per this definition, the diameter of a circle is twice its radius. Alternatively, it could be explained as two radii placed end to end. (Formula for diameter is : d=2r)

Chord: Though a chord is not included in the equation for circumference of a circle, one should be clear about it to avoid confusion with diameter. Like a diameter, a chord is also a straight line that touches any two points of a circle. However, it does not pass though the center of a circle. Conversely, any chord passing through the center of a circle is the diameter.

Pi (π): Pronounced as pie but written pi, π is an irrational number. If written in the form of a decimal it will never end. Hence used in formulas Pi is given the approximate value of 3.14.

Procedure to Find the Circumference of a Circle
The first step to calculate circumference of a circle is to know the formula. There are two formulas that can be used for the purpose. They are:

• Circumference of a circle formula 1: C = π x diameter
• Circumference of a circle formula 2: C = π x 2 radius

The next step is to obtain the values for the radius or diameter of the circle. Write them down on the paper on which you would be recording the value of the circumference. Now plug the values in the formula and calculate the circumference of the circle.

An Example
Here are a few illustrations that would make problem solving related to finding the circumference of a circle easy:

Using the Radius
If the value of the radius is known then it can be put in the 'circumference of a circle equation' already mentioned and the value calculated. For example:
Given that the radius of circle is 3 cm.
Circumference of the circle: C= π x 2 radius
or, C= 3.14 x 2 (3) cm
or, C= 18.84 cm

Using the Diameter
If the value of the diameter is known it can be directly put in the 'circumference of a circle equation' and the circumference calculated. For example:
Given that the diameter of a circle is 6 cm.
Circumference of the circle: C= π x diameter
or, C= 3.14 x 6 cm
or, C= 18.84 cm

Why to Find the Circumference?
Knowing how to calculate circumference of a circle is important as there are quite a few practical applications for it. For example, what if you have a circular garden and you want to lay bricks all around it? You need to know the circumference of your circular garden in order to be able to decide how many bricks to buy. Also tires of vehicles are circular. If there is a particular distance that needs to be covered and if the circumference of the tire is known then it would be possible to calculate the number of rotations of the tire required to cover the distance.

It is not very difficult to learn how to find the circumference of a circle. With the formula and some practice one can easily calculate the rim (circumference) of any circular object.