Board feet measure volume, not length — which is exactly why lumber priced this way can be confusing the first few times you buy it.
Board feet vs. linear feet
A linear foot just measures length, regardless of the board’s thickness or width. A board foot measures the actual volume of wood: a piece 12” long, 12” wide, and 1” thick equals exactly one board foot. Two boards of the same length can contain very different amounts of wood if their thickness or width differs — which is why hardwood suppliers price by board foot instead of length alone.
Why the formula divides by 144
The board foot formula is:
Board feet = (Thickness in inches × Width in inches × Length in inches) ÷ 144
The 144 comes from converting cubic inches into the standard board-foot unit: a 12” × 12” × 1” board contains 144 cubic inches, and that’s defined as one board foot. Dividing your board’s total cubic inches by 144 tells you how many of those “units” it contains.
A worked example
A board that’s 1” thick, 6” wide, and 8 feet (96”) long:
(1 × 6 × 96) ÷ 144 = 4 board feet
If lumber is priced at $4.50 per board foot, that single board costs $18.00 before tax.
Estimating a full project’s cost
Multiply the board-foot count by how many identical pieces you need, then by the price per board foot. Our Board Foot Calculator does this multiplication automatically — enter thickness, width, length, quantity, and price per board foot, and it returns both the per-piece and total board footage along with the estimated cost.
A note on nominal vs. actual dimensions
Softwood dimensional lumber (like a “2x4”) is sold by its nominal size, but the actual finished size is smaller — a 2x4 is really about 1 1/2” × 3 1/2”. Hardwood sold by board foot, on the other hand, is usually priced and measured using its actual rough-cut dimensions. Always confirm which sizing convention your supplier uses before calculating your board footage.