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Or # Radius of a Circle Calculator

Given:

Circumference (c)

Area (A)

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

### How Does This Radius of a Circle Calculator Work?

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

## What is the Radius of a 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” ## How to Find the Radius of a Circle?

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:

### Radius of a Circle Formula:

#### From Diameter: As we know that:

$$Diameter=D=2*r$$
or
$$r=\dfrac{D}{2}$$

#### From Area: You know that:

$$Area=A=𝜋r^{2}$$
or
$$r^{2}=\dfrac{A}{𝜋}) #### From Circumference: As you know that: \(C=2*𝜋*r$$
or
(r=\dfrac{C}{2𝜋}\)

#### From Area and Central Angle of a Sector: You know that:

$$A=\dfrac{\theta}{360^\text{o}}*𝜋*r^{2}$$
or
$$r=sqrt{\dfrac{A*360^\text{o}}{\theta*𝜋}}$$

### Example:

#### Statement:

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

##### Solution:

$$r^{2}=\dfrac{A}{𝜋}$$

$$r^{2}=\dfrac{78}{3.14}$$

$$r^{2}=24.840$$

$$r=\sqrt{24.840}$$

$$r=4.983$$

## References:

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