Circle Circumference Calculator
Compute the circumference of a circle from its radius.
Input Data
Radius
Results
Circumference = 2πr.
31.416
Explanatory note about the result.
周長 = 2πr = 2π·5 = 31.416。
At a glance:Circumference C = 2π·r = π·d. Complements circle-area and circle.
Formula
C = 2π·r.
How to Use
- Enter the radius.
- The tool returns the circumference.
Case Studies
r=3
C = 2π·3 ≈ 18.85.
FAQ
What is π?
The ratio of circumference to diameter, ≈ 3.14159.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.