Radius of a Circle Calculator

Want to calculate the radius of a circle? Cool, try this calculator.

a c b a 2 + b 2 = c 2 a 2 + b 2 = c c 2 - b 2 = a c 2 - a 2 = b a 2 + b 2 = c 2 r d





About This Calculator

This radius of a circle calculator will figure out the radius of any circle given the circumference, the diameter, or the area of the circle.


Terminology

  • "Area" - The amount of surface covered by a two dimensional shape. It is expressed in square units of measurement, for example square feet, square meters, square inches, square yards, etc.

  • "Circumference" - The total distance around the outside edge of a circle.

  • "Diameter" - The distance of a straight line that extends from edge to edge of the circle while passing through the center of the circle.

  • "Radius" - The distance of a straight line that extends from the center of the circle to the edge of the circle.

Calculating the Radius of a Circle Using Circumference

If you know the circumference of a circle, you can calculate the radius based on the following formula:

r = C / 2 ϖ

where

C = Circumference
ϖ = Pi = 3.14159265...
r = Radius


Calculating the Radius of a Circle Using Diameter

If you know the diameter of a circle, you can calculate the circumference based on the following formula. This one's easy, the radius is always half of the diameter:

r = d / 2

where

r = Radius
d = Diameter


Calculating the Radius of a Circle Using Area

If you know the area of a circle, you can calculate the radius based on the following formula:

a c b a 2 + b 2 = c 2 a 2 + b 2 = c c 2 - b 2 = a c 2 - a 2 = b a 2 + b 2 = c 2 r d A = r π A = C 2 π

where

r = Radius
A = Area
ϖ = Pi = 3.14159265...