What is a board foot?
A board foot is a volume of wood 1 inch thick, 12 inches wide and 12 inches long – 144 cubic inches. Hardwood lumber is usually priced per board foot, while construction lumber is often sold per piece.
The board foot formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12. A 2 × 4 that is 8 ft long is 2 × 4 × 8 ÷ 12 = 5.33 board feet. Multiply by the number of boards for the total.
Nominal vs actual size
Board feet are normally calculated with nominal dimensions (2 × 4), not the smaller actual dimensions after planing (1.5 × 3.5 in). Rough hardwood thickness is given in quarters: 4/4 is 1 inch and 8/4 is 2 inches.