Circle Calculator: Find Radius, Area, or Circumference

An online calculator to calculate the area \( A \) , the perimeter \( P \) and the radius \( r \) of a circle given any of these parameters:

Circle Formulas

Given Radius r

\( P = 2 \pi r \) , \( A = \pi r^2 \)

Given Circumference P

\( r = \dfrac{P}{2 \pi} \) , \( A = \dfrac{p^2}{4 \pi} \)

Given Area A

\(r = \sqrt{\dfrac{A}{\pi}} \) , \( P = 2 \sqrt{\pi A} \)

Circle Calculator

Enter any ONE value - radius, circumference, or area

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-- units²
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More References and Links

Grade 8 Problems and Questions on Circles with Answers
Online Geometry Calculators and Solvers