Diameter Calculator: Compute Dimensions of a Circle

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Below is a diameter calculator, which will compute a circle's radius, circumference, and area if you know the diameter.

Do you know a different dimension? Instead try one of the related circle dimension calculators:

Diameter Calculator

What is a Circle's Diameter?

The diameter of a circle is the distance from edge to edge of a circle passing through its origin or center.

Conveniently, it is twice as long as the radius of a circle. If you draw two opposing line segments from the circle's origin to the edge, you just drew the diameter.

Dimensions of a Circle

There are three dimensions most often used to describe a circle:

  • The diameter – defined above
  • The radius – the distance from the circle's center or origin to the edge, one half the diameter
  • The circumference – the length of the outside boundaries of the circle

Starting from the diameter, you can easily find the other two. The next equations show how you can instead find the diameter from them.

The equation for diameter of a circle from circumference is:


If written instead in terms of the radius, the diameter is very simple; it's just twice as long:

d = 2r
Dimensions of a circle: O - origin, R - radius, D - diameter, C - circumference (Wikimedia)

Area is the space contained within the circle's boundaries. It's also easy to find from any of the others.

To find area from the circle's diameter:

a = \pi (d/2)^2

Using the Diameter Calculator

You can enter the diameter and then compute radius and circumference in mils, inches, feet, yards, miles, millimeters, centimeters, meters and kilometers.

Compute the area using these units: square mils, square inches, square feet, square yards, square miles, acres, hectares, square millimeters, square centimeters, square meters, and square kilometers.

To run the calculator, hit the 'Calculate Circle Dimensions' button when you have entered the known diameter.

Did you like this tool? Visit our other calculators and tools.



PK started DQYDJ in 2009 to research and discuss finance and investing and help answer financial questions. He's expanded DQYDJ to build visualizations, calculators, and interactive tools.

PK lives in New Hampshire with his wife, kids, and dog.

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