Circle Measurements Calculator
Table of contents
What are circle measurements? How to measure a circle?How to measure the radius of a circle?How to measure the diameter of a circleHow to measure the circumference of a circle?How to measure the area of a circle?What are the 3D version of a circle?Here are some circlerelated calculatorsFAQsWith 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:

If the diameter is known:
We can calculate the radius,
r
of a circle by dividing its diameter by2
:r = d / 2

If the circumference is known:
The circumference,
c
can be used to calculate the radius using the formula below:r = c / (2 × π)

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:

If the radius is known:
We can calculate the diameter by multiplying the radius by
2
:d = r × 2

If the circumference is known:
The diameter can also be calculated using the circumference:
d = c / π

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:

If the radius is known:
We can use the formula below to calculate the circumference of the circle:
c = 2 × π × r

If the diameter is known:
Using the diameter, we can calculate the circumference as:
c = d × π

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:

If the radius is known:
The area of a circle can be calculated using its radius as follows:
a = π × (r ^ 2)

If the diameter is known:
Using the diameter, the care of a circle can be calculated as follow:
a = (π × d) / 4

If the circumference is known:
The formula below can help you to calculate the circle:
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 the circle also acts as the base of a cone object.
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:
 Determine the radius of the circle
 Apply the circle area formula:
area = 2 × π × r
 Calculate the area of 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.