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Circle Calculator
Enter any one property of a circle — radius, diameter, circumference, or area — and instantly get all the others. Uses π = 3.14159265…
Frequently Asked Questions
From C: r = C / (2π), then A = πr². Example: C = 31.416 → r = 5 → A = 78.54.
How this calculator works
Formula explanation
**r** = radius | **d** = 2r | **C** = 2πr | **A** = πr²
Worked example
**Example:** Radius = 5 → Diameter = 10, Circumference = 31.4159, Area = 78.5398
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