# Radius of a Circle Calculator

Welcome to the **radius of a circle calculator**, where we'll focus on **how to find the radius of a circle from the circumference, area, or diameter**. The concept is not too difficult, and, in essence, it's enough to follow a few simple steps we describe in detail below, all of which take you straight to **a radius of a circle formula**.

## What is the radius of a circle?

By definition, **a circle** is a 2-dimensional shape consisting of all the points lying at the same, fixed distance from a given point. That distance is known as **the radius of the circle**.

Now that we know what the radius of a circle is (marked with green), let's get familiar with the rest of the lines.

**Circumference**(blue) is the perimeter length of the circle.- The
**diameter**(red) is a line with both endpoints on the circle going through the center. **Chord**(purple) is any line with both endpoints on the circle.

In some sense, **the radius is the MVP here**: it plays a crucial role in all the formulas, so it's essential to learn how to find the radius of a circle. Fortunately, the task is relatively simple. After all, since the MVP is in all the equations, we can get the circle radius from the area or the radius of a circle from the circumference.

## How do you find the radius of a circle?

There are three circle radius formulas, depending on what number you know:

**The radius of a circle from the area**: if you know the area`A`

, the radius is`r = √(A / π)`

.**The radius of a circle from circumference**: if you know the circumference`c`

, the radius is`r = c / (2 * π)`

.**The radius of a circle from diameter**: if you know the diameter`d`

, the radius is`r = d / 2`

.

Fortunately, **our radius of a circle calculator handles all of the above cases**. Even better! You don't have to choose which radius of a circle formula you need: simply input the measurement into the tool, and it will automatically process the radius of a circle equation tailored for your needs.

## Other tools like this circle radius calculator

Remember that the radius of a circle calculator is not our only tool dealing with those pesky round objects. Below, we list the others, all ready to **deal with your day-to-day circular problems**.

- Circle calc: find c, d, a, r;
- Circle measurements calculator;
- Circle formula calculator;
- Circle perimeter calculator;
- Circle length calculator;
- Circumference to diameter;
- Diameter of a circle calculator;
- Circumference and area of a circle calculator;
- Square footage of a circle calculator; and
- Square inches of a circle calculator.

## FAQ

### What is the radius of a unit circle?

By definition, a unit circle is a circle with a radius of `1`

. It is a general object used in mathematics (e.g., when explaining trigonometric functions), so the `1`

usually has no unit assigned.

### What is the radius of a 6-foot circle?

To find the radius whose circumference is equal to `6`

feet, we follow the steps below:

**Write**the circumference as`c = 6 ft`

.**Recall**the formula for the radius of a circle from circumference:`r = c / (2 × π)`

.**Inject**the circumference into the equation:`r = (6 ft) / (2 × π) = 3/π ft`

.- If needed,
**substitute**`π ≈ 3.14`

:`r = 3/π ft ≈ 0.96 ft`

.