en.wikipedia.org/wiki/Area_of_a_circle

In geometry, the area enclosed by a circle of radius r is πr2. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter. One method of deriving this formula, which originated with Archimedes, ...

www.mathgoodies.com/lessons/vol2/circle_area.html

Thus, if there were a total of 28.26 squares, the area of this circle would be 28.26 cm2 However, it is easier to use one of the following formulas: Area equals Pi ...

www.khanacademy.org/math/basic-geo/basic-geo-area-and-perimeter/area-circumference-circle/v/area-of-a-circle

The area of a circle is pi times the radius squared (A = π r²). Learn how to use this formula to find the area of a circle when given the diameter.

www.mathwarehouse.com/geometry/circle/area-of-circle.php

Area of a circle, formula for area explained with examples, pictures, interactive examples and quiz.

www.virtualnerd.com/pre-algebra/perimeter-area-volume/circles/circle-sector-area-examples/circle-area-from-diameter

Note: If you have the diameter of a circle, you can use it to find the area of that circle. Just plug that value into the formula for the area of a circle and solve.

www.mathsisfun.com/geometry/circle-area.html

Area of a Circle. Calculator Enter the radius, diameter, circumference or area of a Circle to find the other three. The calculations are done "live":.

www.virtualnerd.com/pre-algebra/perimeter-area-volume/circles/circle-sector-area-examples/circle-area-formula

Virtual Nerd's patent-pending tutorial system provides in-context information, hints, and links to supporting tutorials, synchronized with videos, each 3 to 7 ...

www.wikihow.com/Calculate-the-Area-of-a-Circle

A common problem in geometry class is to have you calculate the area of a circle based on provided information. You need to know the formula for finding the ...

www.calculateme.com/cArea/AreaOfCircle.htm

This calculator will calculate the area of a circle given its radius, using the famous formula area = pi x r squared.