How to calculate the perimeter of a circumference

Calculate the perimeter of a circle can be useful in certain math problems, however, it is not something we usually remember.

Fortunately, we are here to refresh your memory and clear all your doubts about how to calculate the perimeter of a circle. To do this, just apply the following mathematical formula:

Formula to get the perimeter of a circle

To calculate the perimeter of a circumference we need to use a mathematical formula in which the PI number is involved and which is as follows:

L = 2 - π - r

In the above formula we can see that the perimeter of the circle (L) is twice its radius (r) multiplied by the number PI.

It is important that do not confuse radius with diameter since they are different things in which we usually make mistakes. The diameter is twice the measure of the radius of a circle, in the figure that heads this post you can see it represented on a circle so you can see more clearly the difference between radius and diameter.

Note that the perimeter is the length of the figure so that its units will be the same as those of the radius. That is, if you apply the formula for a circumference whose radius is a given number of centimeters, the perimeter will also be in centimeters. If the radius is in meters, the final result will also be in that unit. You can see this more clearly in the practical examples that we propose in the following point.

Exercise to calculate the perimeter of a circle

Perimeter of a circumference

By example,Let's suppose that we want to calculate the perimeter of a circle whose radius is 6 centimeters. In this case, we have that:

L = 2 - π - r = 2 - π - 6 cm = 37.70 centimeters

Yes instead of the radius we have the diameter, la fórmula anterior queda reducida a la siguiente expresión, siendo la variable 'd' el valor del diámetro:

L = π - d

If we apply this new formula with a new practical example we will see it better. Imagine that we have a circumference of diameter 16 centimeters:

L = π - d = π - 16 = 50.27 centimeters

Circumference length calculator

If you want to avoid making operations for find the perimeter of a circleYou can also use our online calculator created especially for this purpose:

Circumference and circle: difference

Perimeter of a circumference

Often the terms are confused with each other. circumference and circle but they really have different meanings. What is the difference?

If we look at the image you have above these lines:

  • The circumference is defined as the flat and closed curve whose points are at equal distance from the center, therefore, it is the line marked in blue.
  • The circle is the area that is contained within a circumference, therefore, it is the surface colored yellow.

We hope that with this explanation you already have a clear understanding of what is the difference between circumference and circle.

Circumference of the earth

Have you ever wondered what is the perimeter of the circumference of the earth? Let's calculate it from the formula we have seen in the theoretical point and knowing that the radius of the earth is 6,371 kilometers:

L = 2 - π - r = 2 - π - 6.371 Km = 40.075 kilometers

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