How to Calculate Board Feet of Lumber

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) × width (in) × length (ft) ÷ 12. If you measure the length in inches instead, divide by 144. For a stack of identical pieces, work out one piece and multiply by the number of pieces.

The formula is the same for every species. What differs is which dimensions go into it: softwood and hardwood are measured by different conventions, covered in the next two sections. The Board Foot Calculator applies the formula to one piece or a stack of identical pieces.

Softwood: nominal thickness and width, actual length

For softwood, the federal definition in the Softwood Lumber Research, Promotion, Consumer Education and Industry Information Order (7 CFR § 1217.4) bases the board-foot calculation for lumber 1 inch or more thick on its nominal thickness and width and its actual length. Softwood with a nominal thickness of less than 1 inch is calculated as 1 inch.

So a 2×4 that has been surfaced to about 1½ × 3½ in is still figured as 2 × 4. An 8 ft 2×4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet.

Hardwood: quarter thickness and a tallied width and length

Hardwood is tallied by the American Hardwood Export Council (AHEC) method: thickness in quarters of an inch (4/4 = 1 in), random widths rounded to the nearest whole inch, and lengths rounded down to the whole foot. A width exactly on the half inch is rounded up and down alternately. AHEC's own example tallies a board 5¼ in wide and 8½ ft long as 5 in × 8 ft.

Example: an 8/4 board, 6¼ in wide and 8 ft 6 in long, is tallied as 2 in × 6 in × 8 ft, so it is 2 × 6 × 8 ÷ 12 = 8 board feet.

Ask whether hardwood is sold on a net tally (measured after kiln drying) or a green tally (measured before). AHEC notes that buyers on a green tally receive roughly 7% fewer board feet, because of shrinkage in the kiln.

To match a hardwood tally in the Board Foot Calculator, enter the quarter thickness as a decimal (5/4 = 1.25), the width rounded to the nearest whole inch and the length rounded down to the whole foot.

Board feet for common sizes

For a given nominal size, board feet per lineal foot = thickness × width ÷ 12, and the total is that figure times the length in feet. The table below works this out for common sizes and lengths.

Nominal vs. actual dimensions

A nominal 2×4 is actually 1.5 × 3.5 inches after milling, and a 1×6 is about ¾ × 5½ in. Board feet for softwood are still figured on the nominal size, so the board-foot total describes the lumber as sold, not the wood volume you end up with. If you need the actual volume — for weight, for example — use the surfaced dimensions instead.