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Created By : Vaibhavi Kumari

Reviewed By : Phani Ponnapalli

Last Updated : May 01, 2023

Circle is a two dimensional closed figure which contains set of all points in the plane which are equidistant from a point called center. The straight line which passes through the center of circle and joins two points on a circle is called diameter. Half of the diameter is called radius.

Radius r
Diameter d
Circumference C
Area A
In Terms of Pi π
Circumference C
Area A

Circle Formulas

The simple and universal formulas to calculate area, circumference and diameter of circle are here

1. Area of Circle Formula:

  • If you know radius,
    • Area A = πr²
  • If you know diameter,
    • Area A = (π/4)d²
  • If you know circumference,
    • Area A = C² / 4π

2. Circumference of Circle Formula:

  • If you know radius,
    • Circumference C = 2πr
  • If you know diameter,
    • Circumference C = πd
  • If you know Area,
    • Circumference C = 2√(πA)

3. Diameter of Circle Formula:

  • If you know radius,
    • Diameter d = r/2
  • If you know Area,
    • Diameter d = (√πA) / 4
  • If you know circumference,
    • Diameter d = C/π

4. Radius of a Circle Formula:

  • If you know diameter,
    • Radius r = 2d
  • If you know Area,
    • Radius r = √(A / π)
  • If you know circumference,
    • Radius r = C/2π

FAQs on Circle Calculator

1. How do you calculate the length of a circle?

Length of a circle is called its circumference which is the total distance around the circle. Multiply the diameter of a circle with π to get its circumference.

2. What is the diameter of circle with radius 20 feet?

Radius of circle r = 20 feet

Diameter formula is d = 2r

d = 2 * 20

Circle diameter = 40 feet

3. How can I use Circle Calculator?

Enter the required credentials in the input sections of the calculator and hit on the calculate button to check radius, diameter, circumference and area of circle as output.

4. What is the diameter of the circle?

Diameter is a line that combines two points on the circle and passes through center. Diameter is double the radius.