Board feet is the measurement of the volume of wood needed for a project. One board foot equals 144 cubic inches of lumber. It is calculated by multiplying thickness by width by length and then dividing the total by 144. For example, if you are using 2 inch thick by 4 inch wide lumber and you need 100 inches of that lumber for your project, you multiply 2 by 4 by 100 for a total of 800. Then, you divide 800 by 144 for a total of 5.5 board feet of lumber.