One board foot is equal to 144 cubic inches of wood. In other words, a board that is 1 inch thick, and 12 inches wide and long contains one board foot of hardwood lumber. ... Hardwood Sizing. Nominal ThicknessS1SS2S 1/2 inch3/8 inch (9.5 mm)5/16 inch (7.9 mm) 5/8 inch1/2 inch (13 mm)7/16 inch (11 mm) 7 more rows Mar 27, 2020