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Math Calculators ▶ Radius of a Circle Calculator

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**Table of Content**

Our radius of a circle calculator mainly functions to find the radius of a circle from the values of circumference, area, or diameter.

Truly uttering, our calculator is pretty easy to use if you stick to the following usage guide!

**Input:**

- From the first drop-down list, select the parameter with which you wish to carry the calculations
- After that, enter its value along with the unit selected from the next list
- At last, hit the “Calculate” button

**Output:**

- Radius, area, diameter, and circumference of the circle

You all may be familiar with a circle, a well-known and widely used geometrical figure.

**“The distance from the center of a circle to any of its points on the circumference is known as the radius”**

In geometry, a circle is defined by many related entities. And if you are willing to find its radius given different parameters, then these include:

As we know that:

\(Diameter=D=2*r\)

or

\(r=\dfrac{D}{2}\)

You know that:

\(Area=A=𝜋r^{2}\)

or

\(r^{2}=\dfrac{A}{𝜋})

As you know that:

\(C=2*𝜋*r\)

or

(r=\dfrac{C}{2𝜋}\)

You know that:

\(A=\dfrac{\theta}{360^\text{o}}*𝜋*r^{2}\)

or

\(r=sqrt{\dfrac{A*360^\text{o}}{\theta*𝜋}}\)

Let us resolve an example that may help you in finding radius of a circle:

What’s the radius of a circle having area as \(78m^{2}\)?

\(r^{2}=\dfrac{A}{𝜋}\)

\(r^{2}=\dfrac{78}{3.14}\)

\(r^{2}=24.840\)

\(r=\sqrt{24.840}\)

\(r=4.983\)

From the source of Wikipedia: Radius, Formula, Use in coordinate systems

From the source of Khan Academy: Radius, diameter, circumference & π, Labeling, Area of parts of circles

From the source of Lumen Learning: Circles, Equation of a Circle in Standard Form, General form of a circle