Circle radius from area calculator
Enter the area of a circle to get its dimensions, useful when you need a circle of a given size and want its radius.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter area (square units) and length unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Radius = √(A ÷ π), diameter = 2 × r and circumference = 2 × √(π × A), where A is the area.
Example
Inputs: Area (square units) = 100, Length unit = Centimeters (cm). Result: Radius: 5.6419 cm; Diameter: 11.2838 cm; Circumference: 35.4491 cm.
Limits and caveats
- Enter the area in the square of the chosen unit; with meters selected the area is in square meters.
Questions about this tool
How do I find the radius from the area?
Divide the area by π and take the square root. An area of 100 cm² gives a radius of about 5.64 cm.
Can I get the circumference straight from the area?
Yes, circumference equals 2 × √(π × A). The tool shows it next to the radius.
If I double the area, does the radius double?
No. The radius grows by √2, about 1.414, because area depends on the radius squared.