How to Calculate Board Feet of Lumber
The volume-based unit lumber is priced and sold by
What a board foot actually measures
A board foot is a volume unit equal to 144 cubic inches — the equivalent of a board 12 inches wide, 12 inches long, and 1 inch thick. It lets lumber of different thicknesses and widths be compared and priced on a consistent basis, unlike a simple linear-foot count which ignores thickness and width entirely.
The formula
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12. All three dimensions come from the board's nominal or actual size, depending on which convention your supplier prices by — hardwood is commonly sold by actual (rough-sawn) dimensions, while dimensional softwood lumber is priced by nominal size.
Nominal vs. actual dimensions
A nominal '2x4' is actually 1.5 × 3.5 inches after milling. Using nominal dimensions in the board-foot formula is standard practice for dimensional softwood lumber pricing, even though the actual finished size is smaller — check which convention your specific supplier uses.
Worked Example
A board 2 in thick, 6 in wide, 8 ft long (nominal dimensions).
Board feet = (2 × 6 × 8) ÷ 12 = 8 board feet