Key takeaways
- A board foot is a volume — 144 cubic inches of lumber, not a length.
- Board feet = thickness(in) × width(in) × length(ft) ÷ 12, times quantity.
- Always figure on nominal dimensions — a 2×4 is priced as 2×4, not its actual 1½ × 3½.
- Hardwood thickness comes in quarters: 4/4 = 1″, 8/4 = 2″, priced per board foot.
How to calculate board feet
Hardwood and rough lumber are sold by the board foot — a volume measure, not a length. A board foot is a volume of lumber equal to 144 cubic inches — a piece 1 inch thick, 12 inches wide, and 1 foot long. To size an order, find the board feet in one piece, multiply by how many you need, then multiply by the price per board foot for a cost.
Always price on nominal (rough-sawn) dimensions — that's how the yard charges, even after surfacing trims the actual size down. A 2×4 is figured as 2 inches by 4 inches, never as its actual surfaced 1½ × 3½ inches.
Worked example: ten 1 × 6 × 8 boards
For one 1″ thick × 6″ wide board running 8 feet long: (1 × 6 × 8) ÷ 12 = 4 board feet each. Order ten of them and that's 4 × 10 = 40 board feet. At $4.50 per board foot, the lumber runs 40 × $4.50 = $180.00 before tax and any surcharges.
Board feet per piece (nominal)
| Board (nominal) | Calculation | Board feet each |
|---|---|---|
| 1 × 6 × 8 ft | (1 × 6 × 8) ÷ 12 | 4.0 |
| 2 × 4 × 8 ft | (2 × 4 × 8) ÷ 12 | 5.33 |
| 2 × 6 × 8 ft | (2 × 6 × 8) ÷ 12 | 8.0 |
| 2 × 8 × 10 ft | (2 × 8 × 10) ÷ 12 | 13.33 |
Buying hardwood by the quarter
Hardwood is often sold in quarter inches of thickness: 4/4 means 1 inch, 6/4 means 1½ inches, and 8/4 means 2 inches, each priced per board foot. Order in nominal thickness so the math matches the yard's invoice, then add a few percent for defects and trimming. Building stairs or a deck frame from the same lumber? Size the run with the stair calculator before you total the order.
Frequently asked questions
What is a board foot?
A board foot is 144 cubic inches of lumber — a piece 1″ thick, 12″ wide, and 1 foot long. It's the unit hardwood is priced in.
How do I calculate board feet?
Thickness × width (inches) × length (feet) ÷ 12, times quantity. A 1×6×8 ft board = 4 bd ft.
How many board feet in a 2x4x8?
Using nominal size, (2 × 4 × 8) ÷ 12 = 5.33 board feet. Figure it on 2×4, not the actual 1½ × 3½.
Nominal or actual dimensions?
Nominal, for pricing. A 2×4 is figured as 2″ × 4″ even though it surfaces down to 1½ × 3½ — that's how yards charge.
What does 4/4 mean?
Quarter inches of thickness: 4/4 = 1″ and 8/4 = 2″. Hardwood is priced per board foot at that nominal thickness.
How much will my order cost?
Total board feet × price per board foot. Ten 1×6×8 boards = 40 bd ft, so at $4.50 that's about $180.
The board-foot definition (144 cubic inches) is the standard lumber unit — see this woodworking reference. Nominal-size pricing follows standard lumberyard practice.
Last reviewed June 2026