Use this radius calculator to compute a circle's diameter, circumference, and area from its radius.
Radius calculator
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Using the calculator
Enter the radius and select your units. The calculator instantly computes the diameter, 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 radius?
The radius of a circle is the distance from its center to the edge. It's exactly half the diameter.
Circle formulas
Given the radius, you can find all other circle dimensions:
d = 2r
c = 2\pi r
a = \pi r^2
