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Math Formulas > Geometry > Area of a Circle

Area of a Circle



r: radius
d: diameter
A: Area

The area of a circle is given by:

A = Π ∙ r2 or A = Π ∙ (d/2)2

Π defines the ratio of any circle's circumference to its diameter and is approximately equal to 3.141593, however the value 3.14 is often used.

Example 1: Determine the area of a circle whose radius is 5 meter.
A = Π ∙ r2 = 3.14 ∙ 52 = 78.5 m2

Example 2: Determine the area of a circle whose diameter is 10 meter.
A = Π ∙ (d/2)2 = 3.14 ∙ (10/2)2 = 78.5 m2
Note that radius = diameter / 2

Online Area Calculator, click on the link will open a new window.

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