How circle calculator works
Calculate circumference and area from a nonnegative radius.
Formula and convention
Diameter = 2r. Circumference = 2πr. Area = πr².A worked example
Radius 5 gives diameter 10, circumference about 31.415927, and area about 78.539816.
Scope and precision
Use one length unit. Area is reported in that unit squared. Displayed values are rounded while calculations use floating-point precision.
Displayed results may be rounded. Inputs are processed locally and are not stored by this site. Keep the original values if you need to reproduce the result.
Why might another tool give a different result?
Compare unit definitions, rounding, period assumptions, and input values. This page states the convention used by this calculator.