# Circle Measurements Calculator

Created by Wei Bin Loo
Reviewed by Dominika Śmiałek, MD, PhD candidate
Last updated: Feb 02, 2023

With this circle measurement calculator, you can easily:

• measure the radius of a circle
• measure the diameter of a circle
• measure the circumference of a circle
• measure the area of a circle

We will also demonstrate some practical examples to help you understand how the circle measurement calculations work using this circle measurement tool.

## What are circle measurements? How to measure a circle?

Circle measurements are numbers that can define a circle. Generally, there are four circle measurements that are essential to understand, namely the radius, diameter, circumference and the area of a circle. Any of them is able to define a circle. Hence, just knowing one of them is enough to calculate the rest of the numbers.

This circle measurements tool is built to help you calculate the circle measurements given that one of them is specified. For instance, this circle measurements calculator can help you to calculate the area, circumference, and diameter of the circle, if you know the radius.

## How to measure the radius of a circle?

We understand how to measure the radius of a circle in three ways:

1. If the diameter is known:

We can calculate the radius, r of a circle by dividing its diameter by 2:

r = d / 2

2. If the circumference is known:

The circumference, c can be used to calculate the radius using the formula below:

r = c / (2 * π)

3. If the area is known:

We can also calculate the radius using the area, a:

r = √(a / π)

## How to measure the diameter of a circle?

Next, let's discuss how to measure the diameter of a circle:

1. If the radius is known:

We can calculate the diameter by multiplying the radius by 2:

d = r * 2

2. If the circumference is known:

The diameter can also be calculated using the circumference:

d = c / π

3. If the area is known:

The formula to calculate the diameter from the area of a circle is:

d = 2 * √(a / π)

## How to measure the circumference of a circle?

Now, let's understand how to measure the circumference of a circle:

1. If the radius is known:

We can use the formula below to calculate the circumference of the circle:

c = 2 * π * r

2. If the diameter is known:

Using the diameter, we can calculate the circumference as:

c = d * π

3. If the area is known:

The formula below allows you to calculate the circumference of a circle using its radius:

c = 2 * π * √(a / π) = 2 * √(a / (π ^ 3))

## How to measure the area of a circle?

Lastly, let's talk about how to measure the area of a circle:

1. If the radius is known:

The area of a circle can be calculated using its radius as follow:

a = π * (r ^ 2)

2. If the diameter is known:

Using the diameter, the care of a circle can be calculated as follow:

a = (π * d) / 4

3. If the circumference is known:

a = c ^ 2 / (4 * π)

## What are the 3D version of a circle?

The most apparent 3D version of a circle is a sphere. A sphere is a perfectly round geometrical object that resembles a ball. Besides the sphere, as a 2D shape, the circle also acts as a component of other 3D objects.

There are two circles at both ends of a cylinder, and circle also acts as the base of a cone object.

Apart from our circle measurement calculator, you may also find some of the circle-related calculators below helpful:

## FAQ

### What is pi (π)?

π is probably the most well known mathematical constant, and the most essential constant in measuring a circle. It can be calculate using the formula below:

π = circumference / diameter

### How to measure the area of a circle?

The area of a circle can be measured in three steps:

1. Determine the radius of the circle
2. Apply the circle area formula: area = 2 * π * r
3. Calculate the area the circle

### Can the radius of a circle be negative?

No, the radius of a circle can never be negative. Although it is mathematically possible, a circle with a engage radius does not exist in our world.

Wei Bin Loo Insert any value below and we will calculate the remaining values for you.
in
Diameter (d)
in
Circumference (c)
in
Area (A)
in²
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