About this Circle Calculator
Circle Calculator combines the three most common circle measurements so you can move from radius to diameter, circumference and area in one step.
Formula or method
Diameter = 2r; Circumference = 2πr; Area = πr².
Example
Radius 5 gives diameter 10, circumference about 31.416 and area about 78.540.
Common uses
- Check geometry homework.
- Estimate circular material dimensions.
- Convert a known radius into other circle measurements.
How to use this tool
- Enter the values or text requested by the calculator.
- Choose units or options when the tool provides them.
- Select the calculation button and review the result.
- Use the formula, example and notes on this page to check whether the result fits your situation.
Important note
All length-based results use the same input unit; area uses the corresponding squared unit.
Frequently asked questions
Which value do I enter?
Enter the radius, which is the distance from the center to the circle edge.
What value of pi is used?
The browser uses its built-in Math.PI constant.