Circle Calculator

Circle Shape

r = radius
C = circumference
A = area
π = pi = 3.14159
√ = square root

Circle Calculator

Use this calculator to find the area, circumference or radius of a circle.  Given any one variable of a circle you can calculate the other 2 unknowns.

* Units: Note that units of length are shown for convenience.  They do not affect the calculations.  The units are in place to give an indication of the order of the results such as ft, ft² or ft³.  Any other base unit can be substituted.

Circle Formulas in terms of Pi π, radius r, and diameter d

Radius and Diameter:

r = d/2

Area of a circle:

A = πr² = πd²/4

Circumference of a circle:

C = 2πr = πd

Circle Calculations:

Using the formulas above and additional formulas you can calculate properties of a given circle for any given variable.

• Calculate A and C | Given r
  Given the radius of a circle calculate the area and circumference
  
  • A = πr²
  • C = 2πr
• Calculate r and C | Given A
  Given the area of a circle calculate the radius and circumference
  
  • r = √(A / π)
  • C = 2πr
• Calculate A and r | Given C
  Given the circumference of a circle calculate the radius and area
  
  • r = C / 2π
  • A = πr²