How to Find the Area of a Circle
Question
The formula for finding the area of the circle is
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How to Find the Area of a Circle

Hi, I'm Jen D'Amore for about.com and this video is all about how to find the area of a circle.
Use Pi to Find the Area of a Circle

There are many practical uses for finding the area of a circle. Finding the area of a square is easy enough, but a circle has curves, which is why we need to involve pi. Pi is that infinite number you'll learn love: 3.141592653589 ... but we'll keep it to 7 decimal places.

If your calculator has a Pi key, you can just use that. That will keep you from typing in all those extra numbers.
Use a Formulate to Find the Area of a Circle

To find the area of a circle, we'll need to also know the radius of the circle. The radius, of course, is half of the diameter. The formula for finding the area of the circle is A = pi(r squared).

A is the area, pi we've covered, and r is of course the radius of the circle.
Examples of Finding the Area of a Circle

So if your circle is 3 feet in diameter, the radius is 1.5 feet. Plug that into the equation to get pi (1.5) squared = 7.07 square feet. If your circle is 20 inches in diameter, then your radius is 10 inches, the formula would be pi x 10 squared = 314.16 square inches.

If your circle is 10 kilometers in diameter, making your radius 5 kilometers, the formula would be: pi x 5 squared = 78.5 square kilometers,

As you can see, it doesn't matter what unit of measurement you're using, inches, feet, miles or meters. you can plug any into the formula to find the area in whatever unit you prefer, as long as you stay consistent.