A board foot is a unit of measurement for the volume of lumber in the United States and Canada. It is used to measure rough lumber or planed/surfaced lumber. One board foot is equivalent to a board that is one inch thick, one foot wide, and one foot long, or 144 cubic inches. Lumber thickness is expressed in quarters of an inch, beginning with 1 inch, so that 1 inch lumber is designated as 4/4, 1-1/2 inch lumber is 6/4, 2 inch lumber is 8/4, and so on. Board footage is calculated by multiplying the length (in feet) by the width (in inches) by the thickness (in inches), and then dividing by 12. For example, a board that is 1 inch thick, 12 inches wide, and 12 inches long is one board foot. It is important to note that nominal lumber includes air space around the physical board when calculating board feet in some situations, while the true measurement of "board feet" should be limited to the actual dimensions of the board.