The formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
Because 12 inches is a foot, this is the same as thickness × width × length (all in inches) ÷ 144. A board 2 inches thick, 6 inches wide and 8 feet long is 2 × 6 × 8 ÷ 12 = 8 board feet.
Why it exists
A tree makes boards of every size. Selling by the piece would make it impossible to compare a thin wide board with a thick narrow one. The board foot is one unit of wood, so a price per board foot means the same whatever the size.
Same board foot, different shapes
Each of these is exactly one board foot:
| Thickness | Width | Length | Board feet |
|---|---|---|---|
| 1 in | 12 in | 1 ft | 1.00 |
| 1 in | 6 in | 2 ft | 1.00 |
| 2 in | 6 in | 1 ft | 1.00 |
| 1 in | 4 in | 3 ft | 1.00 |
| 4 in | 4 in | 9 in | 1.00 |
| 0.5 in | 12 in | 2 ft | 1.00 |
Board feet in common pieces
Using the nominal size, which is how lumberyards price:
| Piece | Board feet |
|---|---|
| 1x6 × 8 ft | 4.00 |
| 1x12 × 8 ft | 8.00 |
| 2x4 × 8 ft | 5.33 |
| 2x6 × 10 ft | 10.00 |
| 2x8 × 12 ft | 16.00 |
| 2x10 × 12 ft | 20.00 |
| 4x4 × 8 ft | 10.67 |
| 6x6 × 12 ft | 36.00 |
Rough, nominal and surfaced
- Hardwood is sold in quarters: 4/4 is 1 inch rough, 8/4 is 2 inches. The board is priced on its rough size even if you buy it planed thinner.
- Softwood framing is priced per piece, but its board feet still use the nominal size, because the name, not the dressed size, is the measure. A 2x4 is 1-1/2 by 3-1/2 inches, yet it counts as 2 by 4.
- Waste is not included. For furniture, plan 20 to 30% extra for defects and offcuts.
Board feet, square feet and linear feet
A square foot is an area and a linear foot is a length. For 1 inch thick boards one board foot equals one square foot, but a 2 inch board covers only half that. Use the board feet to square feet calculator for conversions.
To work out a stack and its cost, use the board foot calculator, or the lumber cost calculator to turn a store price into a price per board foot. Real sizes are in the lumber dimensions chart.
Frequently asked questions
How many board feet are in a 2x4?
0.667 board feet per foot of length, so a 2x4x8 is 5.33 and a 2x4x12 is 8.
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12.
Why is lumber sold by the board foot?
It gives one unit of volume that works for any thickness, width and length, so prices can be compared.