Geometry
Circle Area Calculator
Convert a radius or diameter to area and circumference without re-working the algebra.
circleareacircumference
Circle Area & Circumference
Use radius or diameter inputs and see area plus circumference instantly.
Radius used
7 (unit)
Area
153.94 (unit²)
Circumference
43.98 (unit)
Circle relationships
Area = πr² Circumference = 2πr
The tool converts diameter to radius automatically so you can start from whichever measure is easier to grab.
How to use
- Choose whether you know the radius or the diameter.
- Enter the value and, if desired, adjust the decimal precision.
- Review area in squared units alongside the matching circumference.
Example
Input: Radius = 7 m
Output: Area ≈ 153.94 m², Circumference ≈ 43.98 m
FAQ & notes
Can I enter units like inches or centimeters?
Yes—just stay consistent. Area and circumference mirror the unit you enter (squared or linear).
What if I only have the circumference?
Reverse the process by dividing the circumference by 2π to find the radius, then plug it into the calculator.