of a circle is
I want to calculate

A circle has radius = 13

A = πr2

## Rearranging the equation, we get:

 r2  = A π

 r  = √A √π

 r  = √13 √3.1415926535898

 r  = 3.60555 1.77245

r = 2.0342144725641

## Calculate circumference (C):

C = 2πr
C = 2π * 2.0342144725641
C = 4.0684π or 12.7813

## Calculate diameter (d):

d = 2r
d = 2 * 2.0342144725641
d = 4.0684289451282

r = 2.0342144725641
C = 4.0684π or 12.7813
d = 4.0684289451282

### How does the Circles Calculator work?

Free Circles Calculator - Calculates and solves for Radius, Diameter, Circumference, and Area of a Circle.
This calculator has 1 input.

### What 3 formulas are used for the Circles Calculator?

d=2r
A = 2πr2
C=2πr

For more math formulas, check out our Formula Dossier

### What 7 concepts are covered in the Circles Calculator?

area
Number of square units covering the shape
circle
the set of all points in the plane that are a fixed distance from a fixed point
circles
circumference
the perimeter of a circle or ellips
diameter
distance from two endpoints of a circle through the center
d = 2r
origin
On a two digit coordinate plane, the point (0, 0), where the x-axis and y-axis cross.