Diameter of a Circle Calculator
If you're wondering how to calculate the diameter of a circle, this diameter of a circle calculator is a perfect choice.
You will need either the radius, the circumference, or the area of a given circle for the calculations. Take a look at the picture above the calculator to visualize each element.
How do I calculate the diameter of a circle?
There are three methods for diameter estimation. Choose the useful one based on the data you have. This calculator will automatically estimate all of the other values.

The first one is based on the radius of the circle. The diameter equals the length of two radiuses.
$d=2r$

Area of a circle:
$d=2\sqrt{\frac{a}{π}}$

Circumference of a circle:
$d=\frac{c}{π}$
where:
 $r$ stands for the radius of the circle,
 $c$ for circumference,
 $A$ for area, and
 $d$ stands for the diameter of the circle.
Other circle calculators
If you were looking for the diameter of a circle calculator, here are a couple more tools that may interest you:
 Circle calc: find c, d, a, r
 Circle measurements calculator
 Circle formula calculator
 Radius of a circle calculator
 Circle length calculator
 Circumference and area of a circle calculator
 Circle perimeter calculator
 Circumference to diameter calculator
 Square footage of a circle calculator
 Square inches of a circle calculator
FAQ
What is the diameter of a 9 inch circle?
If the circle radius is 9 inches, then the diameter is 18 inches. The easiest formula for the diameter is d = 2r
, where d
is the diameter and r
is the radius.
How to measure the diameter of a circle?
The diameter is the radius multiplied by two. How to calculate the radius? Measure the distance from the center to any point on the circle.
How do you find the radius and diameter of a circle?
To calculate the radius of a circle, divide its circumference by 2π; for the circle's diameter, divide the circumference by π.
Let's say that the circumference of a given circle is 20 inches. Therefore, its radius is 3.18 in, and its diameter is 6.37 in.