Area is the space covered by a two-dimensional shape. The two dimensions are often expressed in terms of length and height or length and width. Multiplying length by height gives the area of rectangular objects. If these objects are measured in feet, the area is in square feet.
Find the dimensions
Two perpendicular measurements are needed to calculate the area of most shapes. On a rectangle, measuring the sides can give you the dimensions you need because one side can be the length and the adjacent side can be the height. On many other shapes, measuring one or more flat sides and then the height (or greatest distance taken with a perpendicular line) often works.
Plug them into a formula for area
For rectangles, multiply the length (or base) by the width (or height). The units are also multiplied. For example, if you measured a wall at 12 feet long by 8 feet high, the area would be 96 square feet. Use the appropriate formula for the shape. For example, the area of a triangle is the height multiplied by the base and divided by two; the area of a circle is the radius squared multiplied by pi. If the shape is irregular, you may have to calculate the area in segments.
Convert to square feet
If you were working with units other than feet, convert the area to square feet. For example, if you used inches to measure the sides of the object, divide the resulting measurement in square inches by 144 to obtain the area in square feet.