segment in a circle or sphere from its center to its perimeter or surface and its length

In geometry, the radius of a circle or sphere, written as ,[1] is the shortest connection between the center and the boundary. It is either the distance from the center to the perimeter (in the case of a circle), or the distance from the center to the surface (in the case of a sphere). It is half of the diameter.[2] That is, when r is the radius and d is the diameter:[3]

The radius of a circle

r = d ÷ 2

d = 2 x r = r + r

The relationship between the radius and the circumference of a circle is

The area of a circle of radius is

Related pagesEdit


  1. "List of Geometry and Trigonometry Symbols". Math Vault. 2020-04-17. Retrieved 2020-09-24.
  2. Weisstein, Eric W. "Radius". mathworld.wolfram.com. Retrieved 2020-09-24.
  3. "Radius, diameter, & circumference | Circles (article)". Khan Academy. Retrieved 2020-09-24.

Other websitesEdit