The distance from the center of a circle to its perimeter, or from the center of a sphere to its surface. The radius is equal to half the diameter.
Radius
See also
Bertrand's Problem, Circle, Circumference, Conformal Radius, Diameter, Extent, Graph Radius, Inversion Radius, Kinney's Set, Pi, Radius of Convergence, Radius of Curvature, Radius of Gyration, Radius of Torsion, Radius Vector, Sphere Explore this topic in the MathWorld classroomExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Radius." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Radius.html