en.wikipedia.org/wiki/Area_of_a_circle

In geometry, the **area** enclosed by a **circle** of radius r is π r^{2}. 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.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.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":.

virtualnerd.com/geometry/length-area/circles-sectors-area/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.mathwarehouse.com/geometry/circle/area-of-circle.php

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

www.mathgoodies.com/lessons/vol2/circle_area

This relationship is expressed in the following **formula**: diam_formula.gif . **circle**
grid The **area** of a **circle** is the number of square units inside that **circle**. If each ...

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.1728.org/diamform.htm

**Formulas** for **Circle** Circumference, **Circle Area**, Sphere **Area**, Partially Filled
Sphere **Area**, Partially Filled Sphere Volume, Sphere Volume, Cylinder **Area**, ...

www.math.com/tables/geometry/surfareas.htm

In general, the surface **area** is the sum of all the **areas** of all the shapes that cover
the surface of the object. ... That's the **formula for area** of a **circle** (pi r^{2}).