Radius

The radius of a circle

In geometry, the radius of a circle or sphere is the shortest connection between the center and the boundary. It is half of the diameter.

r= d ÷ 2

d= 2 x r = d= r + r

r= Radius d= Diameter

The relationship between the radius $r$ and the circumference $c$ of a circle is $~c = 2\pi r.$

The area $A$ of a circle of radius $r$ is $~A = \pi r^2.$

Related pages

• Area
• Diameter
• Radian

Other websites

• Definition and properties of the radius of a circle with interactive applet