Circle Area Calculator
Calculate the area and circumference of a circle from its radius or diameter instantly, free in your browser.
Enter Values
Shape
How to use this calculator
- Enter the radius.
- Press Calculate for the area.
How it works
The area of a circle is π × radius². The radius is the distance from the centre to the edge.
Worked example
Radius 1 m. Area = π × 1² = 3.1416 m².
Common mistakes
- Entering the diameter instead of the radius — halve the diameter first.
- Squaring the radius wrong: it's radius × radius, not radius × 2.
Frequently asked questions
I only know the diameter — what do I do?
Halve it: radius = diameter ÷ 2. Enter that radius, or use the circle-from-diameter calculator.
What value of π does it use?
Your device's full-precision π, so the area is accurate to many decimal places.
Related tools
- Circumference Calculator
- Cylinder Volume Calculator
- Rectangle Area Calculator
- Triangle Area Calculator
- Cube Volume Calculator
- Sphere Volume Calculator
Explore more in Geometry, Shape, Area & Volume.
Cite this tool
Zerdly. (2026). Circle Area Calculator. Retrieved from https://www.zerdly.com/tools/circle-area-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.