Formula
A board foot is a square foot of wood, one inch thick. In the units a yard writes on a ticket:
board feet = thickness (in) × width (in) × length (ft) × quantity ÷ 12
cost = board feet × (1 + waste) × price per board foot
The same volume in inches is thickness × width × length ÷ 144. A 1 × 12 × 1 is exactly one board foot. That is the hardwood-trade definition, the one the US Forest Products Laboratory uses.
Worked examples
One 2×4×8, nominal. (2 × 4 × 8) / 12 = 5.333 board feet. The dressed 1½ × 3½ stick is 3.5 board feet, and that is not what the softwood yard bills.
10 board feet at $4.50 with 10% waste. You buy 11 board feet. Cost = $49.50. Ten nominal 2×4×8s are 53.333 board feet, $264.00 at the same price and waste.
Reference
One 8-foot stick. Nominal is what dimensional softwood is billed as. Dressed is the size of the stick after the mill planes it, shown so the two numbers stay apart.
| Nominal, 8 ft | Board feet | Dressed size | If billed actual |
|---|---|---|---|
| 1×4 | 2.667 | — | — |
| 1×6 | 4 | — | — |
| 1×8 | 5.333 | — | — |
| 1×10 | 6.667 | — | — |
| 1×12 | 8 | — | — |
| 2×4 | 5.333 | 1.5 × 3.5 | 3.5 |
| 2×6 | 8 | 1.5 × 5.5 | 5.5 |
| 2×8 | 10.667 | 1.5 × 7.25 | 7.25 |
| 2×10 | 13.333 | 1.5 × 9.25 | 9.25 |
| 2×12 | 16 | 1.5 × 11.25 | 11.25 |
Questions
How do you calculate board feet?
Thickness in inches times width in inches times length in feet, divided by 12. A board 1 inch by 12 inches by 1 foot is exactly 1 board foot. Ten feet of that board is 10 board feet.
Is a 2×4 billed as 2 by 4, or as the dressed 1½ by 3½?
Dimensional softwood is billed on the nominal size. A 2×4×8 is (2 × 4 × 8) / 12 = 5.333 board feet, not the dressed stick. Hardwood is often billed on the actual thickness after surfacing. Type the numbers the invoice uses.
How does the waste percentage change the cost?
Cost = board feet × (1 + waste) × price per board foot. Ten board feet at $4.50 with 10% waste is 11 board feet of material, $49.50. The waste is extra stock you buy, not a second markup.
What is a board footage calculator measuring?
The same board foot. “Board feet” and “board footage” are the trade’s two names for thickness × width × length ÷ 12. This page also prices the pile.
Sources
- Board foot = thickness (in) × width (in) × length (ft) ÷ 12. A 1 × 12 × 1 is one board foot.
- Dimensional softwood is sold on nominal size. Hardwood is often sold on the surfaced thickness you actually have.