Use this diameter calculator to compute a circle's radius, circumference, and area from its diameter.
Diameter calculator
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Using the calculator
Enter the diameter and select your units. The calculator instantly computes the radius, circumference, and area in the same units. Supported units include millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles.
Use the Diameter, Radius, Circumference, or Area buttons to switch between calculation modes. Click Show Advanced Options to access arc length, chord length, sector area, and segment area calculations.
What is diameter?
The diameter of a circle is the distance from edge to edge passing through its center. It's twice the length of the radius.
Circle formulas
Given the diameter, you can find all other circle dimensions:
r = d / 2
c = \pi d
a = \pi (d/2)^2
