How To Find The Radius Of A Circle

The major parts of a circle that a student comes across in around 3rd or 4th grade are the Radius Of A Circle, Circumference of a Circle, Diameter of the circle, and the Area of the Circle. The three are a lot different from each other, but what connects them is the measurement of the radius of the given circle. Maybe there are many Radius Of A Circle Calculator on the web, but we don’t need those. The calculation of radius is very easy once you get the basic formulas correct.

So what are we waiting for? Let’s start.

Radius of circle

We will start this tutorial with Definition Of Radius Of Circle

Can you define the radius? Most probably yes. Still, I will explain to you what Radius is. For that look at the image above.

When we draw a circle with a center, say, ‘O’, the radius is the line drawn from this center to its outer edge. So, our line OA is the radius of the circle with measurement = 5 cm.

A radius can be drawn in any direction from the central point.

Radius Of A Circle Formula

When we want to calculate the radius, we must know its relationship with the other parts of the geometry. We must know about the area, diameter, or the circumference of the circle to be able to calculate the diameter.

So, before we start to calculate the radius, we will get familiar with the diameter, circumference, and area of the circle.

  1. The diameter of the circle – The diameter of the circle is the double of the radius. As you see in the diagram, AB is the diameter.

Diameter of Circle


  1. The circumference of the circle – Circumference is the measurement of the outer edge of the circle, starting from one point and coming back to it.

Circumference of Circle

  1. Area of the circle – Area is the space covered by the circle, that is inside of the circle. As you see in the diagram, the shaded part is the area of the circle.

Area Of Circle

Now that the formulas are clear, let’s start with the calculation of radius with examples –

How To Find Radius Of A Circle From Diameter


radius equation using diameter


Let us take a circle with Diameter = 10 cm

How To Find Radius Of A Circle From Circumference


radius equation using circumference


Let us take a circle with Circumference = 15 cm

How To Find Radius Of A Circle From Area


radius equation using area


Let us take a circle with Area = 21 cm2


Here are some more examples for you to practice.

find radius of circle

find radius of circle using area


With the information above, we can say that the radius is actually the distance from the center of the circle to its circumference (edge of the circle). And we can easily find the measure of the radius if we are provided its diameter, area, or circumference.

After reading this post, you must go and try the questions from your textbook, try to solve them and check your answers. If you still find them difficult, we can discuss it again, just comment to me in the comment box.

Hopefully, you liked this tutorial on calculating Radius. If no, please write to me in the comment about your doubts and questions. share this article with your friends to help them with this topic too. You just have to click on the buttons that are given at the end of this article.

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