Circle Area and Circumference Calculator

Calculate circle area, circumference, and diameter from one positive radius using the browser's value of π.

Calculate circle measurements

Area: 78.54Circumference: 31.42Diameter: 10

How this tool works

One radius determines the major measurements of an ideal circle. This calculator reports diameter, circumference, and area together, retaining full floating-point precision internally and rounding only the displayed values.

Diameter equals two times radius, circumference equals two times π times radius, and area equals π times radius squared.

How to use it

  1. Enter a positive radius in any consistent length unit.
  2. Read diameter and circumference in that same length unit.
  3. Treat area as square units corresponding to the entered radius unit.

Worked examples

Radius five

Input
Radius 5
Output
Area 78.54, circumference 31.42

Area multiplies π by twenty-five, while circumference multiplies two, π, and five. Both results are rounded only for display.

Radius ten

Input
Radius 10
Output
Area 314.16, circumference 62.83

Doubling radius doubles circumference but makes area four times larger because the area formula squares the radius.

Limitations

  • Physical measurements and π-based results may require application-specific rounding.
  • The calculator assumes a perfect flat circle rather than an ellipse or irregular boundary.