The formula, and the one that catches people
Thickness (T) and width (W) are in inches; length (L) is in feet. A board foot is one piece 1 inch thick, 12 inches wide and 12 inches long — exactly 144 cubic inches. If your length is in inches rather than feet, divide by 144 instead of 12.
Nominal vs actual — the gotcha
Board feet are always figured from the nominal size, not what the board actually measures. A "2 by 4" is planed down to 1.5 by 3.5 inches, but it still counts as a full 2 by 4 in board feet. Use the actual dimensions and you undercount every time.
You pay for the nominal 2×4 and receive a 1.5×3.5. Board feet always use the nominal size, so a 2x4x8 is 5.33 BF, not the 3.5 BF the finished dimensions would suggest.
Board feet for common sizes
| Board (nominal) | Length | Board feet |
|---|---|---|
| 1 × 6 | 8 ft | 4.0 |
| 1 × 12 | 8 ft | 8.0 |
| 2 × 4 | 8 ft | 5.33 |
| 2 × 4 | 12 ft | 8.0 |
| 2 × 6 | 8 ft | 8.0 |
| 2 × 8 | 8 ft | 10.67 |
| 2 × 10 | 8 ft | 13.33 |
| 2 × 12 | 8 ft | 16.0 |
| 4 × 4 | 8 ft | 10.67 |
| 6 × 6 | 8 ft | 24.0 |
One cubic foot is 12 board feet, which is handy for large orders. Lumber is priced by the MBF (1,000 board feet), so $700/MBF is $0.70 a board foot.
Buying by board feet without getting short
- Add a waste factor. For hardwood projects, order 15–25% more than the finished board feet to cover cuts, defects, and offcuts.
- Hardwood uses quarters. Rough hardwood thickness is written in quarter-inches: 4/4 is 1 inch, 5/4 is 1.25, 8/4 is 2. It is counted from that rough nominal size, not the surfaced thickness.
- Board feet, not linear feet. Home-center softwood is often priced per linear foot; a lumber yard prices hardwood per board foot. Do not mix the two when comparing.
Common questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2 by 6 board that is 8 feet long is (2 x 6 x 8) divided by 12, which is 8 board feet. If the length is in inches instead, divide by 144.
Do you use nominal or actual dimensions?
Nominal. A board sold as a 2 by 4 is counted as 2 inches by 4 inches for board feet, even though it actually measures 1.5 by 3.5 inches. That is the industry standard: you pay for the nominal size.
How many board feet are in a 2x4x8?
5.33 board feet, from (2 x 4 x 8) divided by 12. A 2x6x8 is 8 board feet, and a 2x12x8 is 16.
What is the difference between board feet and linear feet?
A linear foot measures only length; a board foot measures volume (144 cubic inches). An 8-foot 2 by 6 is 8 linear feet but 8 board feet, while an 8-foot 2 by 12 is still 8 linear feet but 16 board feet.
