Square feet is an area measurement, and it is used to measure the area of houses, countertops, wall coverings, backyards and just about anything else. You can easily calculate the area in square feet by recognizing standard shapes, such as circles, triangles and rectangles, and then applying the applicable formula.
Calculate the area of a rectangle by multiplying its length by its width. As an example, a rectangular room measuring 10 feet by 8 feet has an area of 80 square feet.
Calculate the area of a triangle by multiplying its base by its height and dividing by two. As an example, if the triangular section under your roofs measures 10 feet across the bottom (the base), and the top peak (height) measures 8 feet above that, then you would multiply 8 by 10 and divide it by 2. This gives you an area of 40 square feet.
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Calculate the area of a circle by squaring the radius, or the distance from the center to the outside edge, and multiplying it by 3.14. As an example, the surface area of your circular swimming pool can be calculated by squaring the 8-foot radius and then multiplying it by 3.14. This gives you a surface area of 201 square feet.