Enter any one circle measurement — radius, circumference, or area — and the Diameter Calculator works out the diameter along with all other circle properties. Pick your known value, type it in, and get the full set of results: diameter, radius, circumference, and area in one go.
Diameter
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Radius
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Circumference
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Area
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The diameter is simply twice the radius: D = 2r. For example, if the radius is 7 units, the diameter is 14 units. The radius is always exactly half of the diameter.
Use the formula D = C / π, where C is the circumference and π ≈ 3.14159. For instance, a circle with a circumference of 44 units has a diameter of approximately 14.006 units.
First find the radius using r = √(A / π), then double it: D = 2 × √(A / π). If the area is 154 square units, the diameter works out to approximately 14.006 units.
Pi (π) is a mathematical constant approximately equal to 3.14159265. It represents the ratio of a circle's circumference to its diameter and appears in all circle formulas because this ratio is the same for every circle, regardless of size.
The radius is the distance from the center of a circle to any point on its edge. The diameter is the longest straight line that can be drawn across a circle, passing through the center — it equals exactly twice the radius.
Yes. Since area A = π × r², you can rearrange to get r = √(A / π), and then multiply by 2 to get the diameter. This calculator handles that conversion automatically.
The calculator is unit-agnostic — you can enter values in any unit (centimeters, meters, inches, feet, etc.). The output will be in the same unit you entered. Just make sure all your measurements use the same unit system.
By definition, the diameter is the largest chord of a circle — a straight line segment connecting two points on the circle. The longest such line must pass through the center, because any line not through the center would be shorter than one that does.