Circle circumference
Calculate the circumference of a circle from its radius. See the formula using pi, input units and a worked example.
Inputs
Use the units shown—
Enter your values and select Calculate.
Formula & explanation
C = 2πr
Variables & units
- Radius
- cm · minimum 0, maximum 1000000000
Worked example
A radius of 3 cm gives a circumference of approximately 18.849556 cm.
Assumptions
Radius is half the diameter.
Formula version 1.0.0. JavaScript floating-point arithmetic applies. Results display up to 6 decimal places; stored values retain available precision. Use the units shown.
Practice with an example
Use the default input values to find the answer. The reset icon restores those values.
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