Finding the area of a shape is very simple, as long as you know the proper formula. The most common shapes to find the area of are rectangles and circles. Each of these shapes has its own distinct area formula. To find the area of a circle, you will need to use a calculator that has a button for pi. If you are using a calculator that does not have this button, you can approximate the area by substituting 3.1415 for pi.
Multiply the length of a rectangle by its width to find its area. For example, if a rectangle has a length of 7 feet and a width of 4 feet, its area is 28 square feet.
Divide a circle's diameter by 2. This will give you its radius. For example, if a circle has a diameter of 20 feet, its radius is 10 feet.
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Square the circle's radius, which means multiply it by itself. Using the example, 10 x 10 = 100.
Multiply the number obtained in Step 3 by pi. This will give you the area of the circle (100 x pi= 314.15 square feet).