How to calculate board feet
A board foot is a volume of lumber — 144 cubic inches, or a piece 1 in thick by 12 in by 12 in. The quick formula keeps length in feet:
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
Multiply by the number of boards for the total. A board 1 in × 6 in × 8 ft is 1 × 6 × 8 ÷ 12 = 4 board feet, so ten of them is 40 board feet. Hardwood is sold this way, so the board-foot total — not the linear feet — is what you price.
Quarter (4/4) thickness sizing
Rough hardwood thickness is written in quarters of an inch. Pricing uses the rough thickness, even though surfaced boards end up thinner.
| Called | Rough thickness | Surfaced (S2S) |
|---|---|---|
| 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 |
Good to know
- Board feet ≠ linear feet. Linear feet is just length; board feet folds in thickness and width too.
- Price on rough size. Hardwood is measured before surfacing, so a planed 4/4 board is still sold as a full inch thick.
- Buy extra. Add 15–20% for knots, checks, and offcuts — more for figured or narrow stock.
- Mind the grade. Higher grades yield more usable wood per board foot; rustic grades need more buying.