What is the Area of a Circle Calculator?
Calculate the area, circumference and diameter of a circle from its radius. These geometry calculators work out area, perimeter, volume and surface area for common shapes. Units are flexible — enter every length in the same unit and the answer comes back in that unit (squared or cubed).
How to use the Area of a Circle Calculator
- Enter your radius.
- Results update automatically as you type; you can also press Calculate.
- Read the output: area, circumference, diameter.
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With radius = 5, the Area of a Circle Calculator returns area: 78.5398163397; circumference: 31.4159265359; diameter: 10.
Tips for better results
- Keep all measurements in one unit before calculating.
- Area units are squared (m², ft²) and volume units are cubed (m³, ft³).
- Use our area and volume converters to switch units afterwards.
Frequently asked questions
What does the Area of a Circle Calculator do?
Calculate the area, circumference and diameter of a circle from its radius.
How is it calculated?
The Area of a Circle Calculator uses this method: A = πr²; C = 2πr.
Can you show an example?
With radius = 5, the Area of a Circle Calculator returns area: 78.5398163397; circumference: 31.4159265359; diameter: 10.
Is the Area of a Circle Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the Area of a Circle Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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