Mostly used in the US, board footage is a unit to measure the volume of lumber. One board foot is equivalent to the volume of a board 1 ft long, 1 ft wide, and 1 in. thick. In practice, nominal thickness and width and the actual length are used for the lumber that is 1 in. or more in thickness. Nominal thicknesses of less than 1 in. are calculated as 1 in.