How many board feet in a hardwood board
Hardwood is sold by the quarter: 4/4 is a board 1 in thick rough, 5/4 is 1¼ in, 8/4 is 2 in. Its board feet are the thickness in inches times the width in inches times the length in feet, over 12. A 4/4 board 7½ in wide and 9 ft 6 in long is 1 × 7½ × 9.5 ÷ 12 = 5.94 board feet.
A hardwood yard does not bill 5.94. It tallies the board the way the National Hardwood Lumber Association's rules say: the length drops to the whole foot below, 9 ft; the width times those feet over 12 is the surface measure, 7½ × 9 ÷ 12 = 5.625, rounded to the nearest whole square foot, 6; and the board feet are that times the thickness. The ticket says 6 board feet. This page prints both, the exact figure and the tally, and "Hardwood quarters, NHLA tally" under "Measure the boards by" prices the tally.
Two details of the rules change a ticket. A board that comes to exactly half a square foot is counted up, and the next one down, in turn through the tally — not every half up, as one supplier's guide says. And lumber thinner than an inch is measured as an inch: a 3/4 in board 6 in wide and 8 ft long is 4 board feet, not 3. One calculator rounds every thickness up to the next quarter instead; a rough 4/4 board that measures 1⅛ in would become 5/4.
Paid for at the quarter, planed thinner
Surfaced two sides (S2S), a board loses 3/16 in up to 6/4 and ¼ in from 8/4, and its board feet are still counted at the rough quarter. The 4/4 board above is 13/16 in thick planed: 4.82 board feet of wood, billed as 6.
| Quarter | Rough | Surfaced two sides |
|---|---|---|
| 4/4 | 1 in | 13/16 in |
| 5/4 | 1¼ in | 1 1/16 in |
| 6/4 | 1½ in | 1 5/16 in |
| 8/4 | 2 in | 1¾ in |
| 12/4 | 3 in | 2¾ in |
| 16/4 | 4 in | 3¾ in |
The thickness box reads the quarters as written: type 4/4, 5/4 or 8/4. It refuses 11/4, which is no thickness a yard sells and may be 1 1/4 typed without its space.
How much to buy
Rough hardwood loses more to knots, checks and saw cuts than surfaced softwood: the page starts at 10%, and one supplier's guide adds 25 to 30% for furniture and 15 to 20% for glue-ups. Type yours. The list counts whole board feet to pick boards to: 5.94 with 10% is 6.53, so 7.