What is a board foot?
A board foot is a volume of wood: 1 inch thick, 12 inches wide and 12 inches long. That's 144 cubic inches. Lumberyards use it to price hardwoods and rough-sawn stock, because those boards come in random widths and lengths that don't fit a simple per-piece price.
The board foot formula
With thickness and width in inches and length in feet, the formula is:
Board feet = thickness × width × length ÷ 12
If you measure everything in inches, divide by 144 instead. Multiply by the number of boards for a stack.
Worked examples
- One 1 × 6 board, 8 ft long: 1 × 6 × 8 ÷ 12 = 4 board feet
- Ten 2 × 4s, 8 ft long: 2 × 4 × 8 ÷ 12 × 10 = 53.3 board feet
- One 8/4 walnut board, 7 in wide, 6 ft long: 2 × 7 × 6 ÷ 12 = 7 board feet
Nominal or actual size?
Hardwood dealers usually figure board feet from the rough thickness, written in quarters: 4/4 is 1 inch, 5/4 is 1¼ inches and 8/4 is 2 inches. A board planed down after sale still counts at its rough size. For softwood framing lumber, most people use the nominal size, so a 2 × 4 counts as 2 by 4 inches even though it measures about 1½ by 3½.
Whatever you use, use it the same way for every board, and ask your supplier which they quote.
Tips for buying lumber
- Add 15 to 20 percent for knots, checks and cuts when buying rough hardwood for furniture.
- Lengths are usually rounded down to the nearest foot and widths to the nearest half inch on rough stock.
- For framing and decks, you usually buy by the piece. Use the deck board calculator to count boards.
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 1 by 6 board that's 8 feet long is 4 board feet.
How many board feet are in a 2x4x8?
Using nominal size, 2 times 4 times 8 divided by 12 is 5.33 board feet.
Is a board foot the same as a linear foot?
No. A linear foot is just length. A board foot is a volume that also counts thickness and width, so a wide, thick board has more board feet per linear foot.
What does 4/4 and 8/4 mean in lumber?
It's the rough thickness in quarters of an inch. 4/4 is 1 inch, 6/4 is 1.5 inches and 8/4 is 2 inches.
Sources
Results are estimates for planning. Product coverage, site conditions and installation methods vary, so check manufacturer guidance before you buy.