How to work out board feet
A board foot is a piece of wood 12 in long, 12 in wide and 1 in thick. Multiply the thickness, the width and the length in inches and divide by 144. Five boards 1¼ in thick, 10 in wide and 8 ft long are 1¼ × 10 × 96 ÷ 144 = 8.333 board feet each, 41.67 for the five. At $4.15 a board foot that is $172.92. Keep every decimal until the end: one calculator rounds to 41.67 first and gets $172.93.
Type the length the way a yard says it. A bare 8 in the length box is 8 ft, and 8' 6" or 102in read as well. One calculator wants 96 for an 8 ft board; another refuses 8' 6".
Which size you pay for
Softwood is billed by its nominal size, the name on the tag, and its board feet are counted on that name: the American Softwood Lumber Standard, PS 20, says so in as many words. A 2×4 is really 1½ in by 3½ in once it is dried and planed, so a 2×4 8 ft long is 5.33 board feet on the invoice and 3.5 board feet of wood. One calculator's table counts the first without saying which; another prints 5.34. This page prints both, each saying which size it is.
The five 5/4×10 boards above are dressed to 1 in by 9¼ in: they hold 30.83 board feet of the 41.67 you pay for.
| Nominal | Dressed, dry |
|---|---|
| 1 in board | ¾ in |
| 5/4 board | 1 in |
| 2 in to 7 in | ½ in less: 2×4 is 1½ × 3½ |
| 8 in and wider | ¾ in less: 2×10 is 1½ × 9¼ |
| Timbers, 5 in and up | ½ in less, green: 6×6 is 5½ × 5½ |
Hardwood is sold by the quarter instead — 4/4, 5/4, 8/4 — and a hardwood yard tallies it by its own rules: the hardwood board foot calculator works them. The thickness box here reads 5/4 as written too. For wood you have measured with a tape — reclaimed boards, a slab — choose Actual size under "Measure the boards by".
Waste, and the list to buy
No calculator we checked adds any waste. This one adds 10%, the low end of the 10–15% suppliers add for surfaced stock, for knots, checks and saw cuts. The five boards become six on the list. Softwood is listed by the board, at the shortest length a yard sells that holds yours, 8 ft to 20 ft in 2 ft steps; anything measured as it is, by the board foot.
Big orders are quoted by the thousand board feet, MBF: $4.15 a board foot is $4,150 an MBF. Type a price per board foot, per linear foot or per board, and the answer says it the other ways too.