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Area of a Circle (Definition and Formula)

A circle is the collection of all points in a plane that are equidistant from a fixed point in the plane.
The fixed point is called the center of the circle.

Area of circle

Circumference: The perimeter of a circle is called Circumference. See fig.(c).

Circumference = π × Diameter

Circumference = 2 × π × Radius

 Radius: The distance from the center to a point on the circle is called the radius of the circle. Radius denoted by r. See fig.(a).

Diameter: A chord of a circle passing through its center is called a diameter of the circle.  Diameter  is the longest chord of a circle. It is denoted by D. See fig.(b).

note, diameter  is always twice the Radius. Diameter  formula is here:

Diameter = 2 × Radius

Radius, Diameter and Circumference

Area of circle



What is the area of circle?

The area of circle is multiplication of π and the the squared of radius, which is written as:

A = π r2


  • A is the area
  • r is the radius of the circle
  • The value of  π is equal to 3.14 or 22/7

Example: What is the area of a circle with radius of 10.5 m ?

As we know, Area = πr2
= π × 10.52
= 3.14 × (10.5 × 10.5)
= 346.18 (to 2 decimals)

Or if we know Diameter then,


Area of circle = (π/4) × D2