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| Area of a
Circle
Part I |
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Unit 2
> Lesson 3 of 6 |
The distance around a
circle
is called its circumference. The distance across a circle through its center
is called its diameter. We use the Greek letter 
(pronounced Pi) to
represent the ratio of the circumference of a circle to the diameter. In the last lesson, we learned that
the formula for circumference of a circle is:
 . For simplicity, we
use = 3.14.
We know from the last lesson that the diameter of a circle is twice as long as the
radius.
This relationship is expressed in the following formula: ![[IMAGE]](images/diam_formula.gif) .
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 ![[IMAGE]](images/circle_parts.gif)
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![[IMAGE]](images/circle_grid.gif)
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The area of a circle is the number of square units inside that circle. If each square in the circle to the left has an area
of 1 cm2, you could count the total number of squares to get the area of this circle. 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:
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or
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where  is the area, and  is the radius. Let's look at some examples involving the area of a circle. In each of the three examples below, we will
use = 3.14 in our calculations.
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