This area of a circle calculator computes the area, radius, or diameter of a circle from any one of those values.
Math
Area of a Circle Calculator
Calculate the area of a circle from radius, diameter, or area.
Calculator
About this calculator
Formula notes
Area = πr²; diameter = 2r; r = √(area/π).
Worked examples
- Example: a circle with a 10 cm radius has an area of about 314.16 cm².
- A circular garden with a 2 m radius has an area of about 12.57 m².
How to use it
- Enter radius, diameter, or area.
- Leave the other fields empty.
- Read the remaining circle measurements.
Frequently asked questions
Which unit should I enter?
Use any supported length unit; the area result matches the square of that unit (for example cm produces cm²).
Can I start from the area?
Yes. Enter the area and the calculator will derive the radius and diameter.
Limits and interpretation
- The calculator assumes a perfect circle; irregular or oval shapes need a different method.
- Unit precision matters: entering the radius in cm changes the area to cm².