Circle Calculator — Area and Circumference
Calculate circle area (πr²) and circumference (2πr) from the radius. Example: r=7 → area ≈ 153.94, circumference ≈ 43.98. Browser-only geometry with a clear formula check.
How it works
Enter the radius. Results use the browser Math.PI constant.
Formula
A=πr²; C=2πr. Notes:
- Diameter is not a separate input — use r = d/2.
- Units are those of r, squared for area.
- Pair with triangle / volume tools.
Example
Example: r=7 → area ≈ 153.94, circumference ≈ 43.98.
When to use it
- Geometry homework.
- Quick circle check.
- Compare related shape tools.
Frequently asked questions
Sample?
r=7 → ≈153.94 and ≈43.98.
Diameter?
Halve it to get r.
Exact π?
Uses Math.PI.
Advice?
Educational only.
Related tools
Questions or feedback
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