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 |
Board feet, linear feet, and nominal size
Three different ways lumber is measured trip people up:
- Board feet — volume (thickness × width × length). How rough hardwood is sold.
- Linear feet — length only, for a single known profile (trim, dowels, dimensional softwood).
- Nominal size — the "2×4" name, which is bigger than the actual planed size (a 2×4 is really 1½ × 3½ in). Softwood framing is sold this way, by the piece.
Hardwood grades (NHLA)
Grade describes how much clear, defect-free wood a board yields — it changes the price per board foot a lot:
| Grade | Roughly |
|---|---|
| FAS (Firsts & Seconds) | Best — long, wide clear cuttings |
| Select | One good face; great value |
| #1 Common | "Cabinet grade" — smaller clear parts |
| #2 Common | Rustic; fine for small or painted parts |
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, or a lower grade.
- Mind the grade. Higher grades yield more usable wood per board foot; rustic grades need more buying.
Why hardwood is sold by the board foot
Softwood framing comes in tidy, uniform sizes — a 2×4 is a 2×4 — so it's sold by the piece or the linear foot. Rough hardwood doesn't work that way: boards come in random widths and lengths straight off the log, so the only fair way to price them is by volume, and the board foot is that unit. The lumberyard tallies each board's thickness, width, and length, adds them up, and multiplies by the price per board foot for the species and grade.
Estimating board feet for a project
To budget a build, list each part's rough thickness, width, and length, run each through the board-foot formula, and total them. Then add 15–20% waste — more for narrow rips, curved parts, or a lower grade — because rough boards lose size when you joint and plane them, and you'll cut around defects. Buying a little long and wide on the rough stock is always cheaper than coming up short mid-project.