Radius of a Circle

on . Posted in Plane Geometry

Radius, abbreviated as r, of a circle is a fundamental geometric property that defines the distance between the center of the circle and any point on its circumference.  It is a line segment between the center point and a point on a circle or sphere.

Radius is used in many practical applications, ranging from mathematics and geometry to engineering, physics, and everyday life.  It helps define and calculate various aspects of circles, including their size, shape, and proportions.


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Radius of a Circle formula

\(\large{ r = \frac{C}{2 \; \pi} }\)     (Radius of a Circle)

\(\large{ C =  2 \; \pi \; r  }\) 

Solve for r

circumference, C

Solve for C

radius, r

Symbol English Metric
\(\large{ r }\) = radius \(\large{ in }\) \(\large{ mm }\)
\(\large{ C }\) = circumference \(\large{ in }\) \(\large{ mm }\)
\(\large{ \pi }\) = Pi \(\large{3.141 592 653 ...}\)


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