Circle Circumference Calculator
Circle circumference calculator
Compute circumference of a circle from radius.
InputsForm1 fieldLive
Result
31.41592654
Using C = 2 × pi × r.
Live update
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Formula
C = 2 x pi x r Symbol legend
| Symbol | Meaning | Unit | Copy |
|---|---|---|---|
C | Circle circumference | length | |
r | Circle radius | length | |
\pi | Pi constant | - |
- Multiply radius by 2.
- Multiply by pi to get circumference.
- Keep units in linear length (not squared).
Example
Worked example: r = 5
- 1 2 x r = 10
- 2 C = 10 x pi
- 3 C = 31.4159
The circumference is about 31.4159 units.
How
- Enter the circle radius.
- Read the live circumference output.
- Copy the result for downstream calculations.
Avoid
- Using area formula pi r^2 when circumference is needed.
- Using diameter in place of radius without adjustment.
- Reporting circumference in square units by mistake.
FAQ
Can I calculate circumference from diameter?
Yes. Convert diameter to radius first (r = d/2), or apply C = pi d manually.
What unit is used for circumference?
It uses the same linear unit as the input radius.
Does this tool round the result?
It displays a rounded view, but underlying calculations preserve precision.
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