Circle area and circumference
Enter a radius to find a circle’s area, circumference and diameter. Compare round table tops, circular layouts or geometric exercises. The radius runs from the center to the edge; it is half the diameter.
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Your inputs
The editable example is illustrative. Enter your own dimensions, operating data, prices, and fees. Results update as you edit.
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How it works
- Area = π × ²
- Circumference = 2 × π ×
- Diameter = 2 ×
- Worked example
- r = 5 m → 25π m²; 10π m; 10 m
Input and formula key
Your result
Complete the inputs to see your result.
Assumptions and limitations
The radius is positive and entered in metres. Outputs describe an ideal flat circle, not an ellipse or a curved surface. Area is in square metres; circumference and diameter are in metres. Internal calculations retain more precision than the displayed result.
Sources
- OpenStax — mathematical formulas Sources reviewed: 2026-10-28
Processing and privacy
The calculation or transformation runs in your browser. The tool does not send its input values or generated output to an application server. Loading a page still makes infrastructure requests; optional analytics and Google consent messages have separate controls.
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Sources and maintenance
Maintained by emonster. Sources are listed with their own review dates; these are not live-data timestamps or claims of independent expert certification.
