How board feet are calculated
A board foot is a volume: a piece 1 in thick, 12 in wide and 12 in long, or 144 cubic inches. Because thickness and width are measured in inches and length in feet, the 144 shrinks to a divisor of 12.
board feet per board = thickness (in) × width (in) × length (ft) ÷ 12
total board feet = board feet per board × number of boards, added up over every board size
lineal feet = length (ft) × number of boards
cubic feet = total board feet ÷ 12
cost = total board feet × price per board foot
The calculator uses the dimensions you type. Enter nominal sizes to match how a lumberyard prices framing lumber, or actual sizes if you want the true volume of wood.
Worked example: 10 boards, 2 × 4 in × 8 ft
The calculator opens on 10 boards of 2 × 4 in, 8 ft long: a stack of 2×4×8 studs counted by nominal size.
- One board: 2 × 4 × 8 = 64; 64 ÷ 12 = 5.333 board feet.
- The order: 5.333 × 10 = 53.33 board feet.
- Lineal feet: 8 ft × 10 = 80 ft.
- Cubic feet: 53.33 ÷ 12 = 4.444 ft³.
Add a price per board foot under advanced options to see the cost. At $4.50 per board foot, a 4/4 board 6 in wide and 10 ft long (5 board feet) costs $22.50.
Nominal vs actual lumber sizes
A 2×4 is not 2 in by 4 in. Softwood lumber is named by its rough, nominal size and then dried and planed to a smaller dressed size. Yards still count board feet by the nominal size, so a 2×4×8 bills as 5.33 board feet even though the wood in it is 3.50 board feet, about 66% of the nominal figure.
| Nominal | Actual size | bf per ft | 8 ft nominal | 8 ft actual |
|---|---|---|---|---|
| 2×4 | 1-1/2 × 3-1/2 in | 0.667 | 5.33 | 3.50 |
| 2×6 | 1-1/2 × 5-1/2 in | 1.000 | 8.00 | 5.50 |
| 2×8 | 1-1/2 × 7-1/4 in | 1.333 | 10.67 | 7.25 |
| 2×10 | 1-1/2 × 9-1/4 in | 1.667 | 13.33 | 9.25 |
| 2×12 | 1-1/2 × 11-1/4 in | 2.000 | 16.00 | 11.25 |
| 4×4 | 3-1/2 × 3-1/2 in | 1.333 | 10.67 | 8.17 |
| 6×6 | 5-1/2 × 5-1/2 in | 3.000 | 24.00 | 20.17 |
Dressed dry sizes per PS 20, American Softwood Lumber Standard. The bf per ft and 8 ft columns are board feet (thickness × width × length ÷ 12); the actual column uses dressed sizes.
If you type an actual size such as 1.5 or 5.5, the calculator flags it, because a yard quote based on nominal sizes will not match your number.
Buying hardwood by the board foot
Hardwood dealers sell rough lumber by the board foot, with thickness in quarters of an inch: 4/4 = 1 in, 5/4 = 1-1/4 in, 6/4 = 1-1/2 in, 8/4 = 2 in, 12/4 = 3 in, 16/4 = 4 in. The board is billed at its rough quarter thickness even if you have it surfaced, so a 4/4 board planed thinner still counts as 1 in.
- Hardwood often comes in random widths and lengths. Measure each board's width and length and enter each one with “+ Add another board size”, or group boards of the same size under one quantity. The board feet are totalled for the whole list.
- Enter thickness in inches: 1 for 4/4, 1.25 for 5/4, 2 for 8/4.
- Thin stock is usually still counted at 4/4. The calculator warns when a narrow board is under 1 in thick.
- Buy extra for knots, checks, splits and offcuts. Pick boards first, then total them, so the quote matches what goes on the truck.
- Compare prices on the same basis. A price per lineal foot can be converted with the board feet per foot column in the table above.
Sources
- Definition: 1 board foot = 144 in³, a board 1 in × 12 in × 12 in; board feet = thickness (in) × width (in) × length (ft) ÷ 12
- Trade convention: dimensional lumber is counted by nominal size; rough hardwood is sold by nominal quarters (4/4 = 1 in, 5/4 = 1¼ in, 6/4, 8/4 = 2 in)
- U.S. Department of Commerce, NIST, Voluntary Product Standard PS 20, American Softwood Lumber Standard (dressed sizes of dimension lumber)