What a board foot is
A board foot is the standard unit of lumber volume in North America: a piece 1 in thick, 12 in wide and 1 ft long, or 144 cubic inches. Hardwoods, live-edge slabs and rough sawn lumber are priced by the board foot, while construction lumber at home centers is usually priced by the piece. Converting to board feet lets you compare prices fairly and estimate a load before you go to the lumberyard.
The formula
- Board feet = thickness (in) × width (in) × length (ft) ÷ 12
- Cost = board feet × price per board foot
- 12 board feet = 1 cubic foot; 1 cubic meter ≈ 424 board feet
Use nominal sizes for dimensional lumber: a 2 × 4 counts as 2 × 4 in even though it is planed to 1½ × 3½. Rough hardwood is sold by thickness in quarters: 4/4 is 1 in, 5/4 is 1¼ in, 8/4 is 2 in.
Worked example
A woodworker buys ten 4/4 red oak boards, 6 in wide and 8 ft long, at $6.50 per board foot.
- Each board: 1 × 6 × 8 ÷ 12 = 4 board feet.
- Ten boards: 40 board feet.
- Cost: 40 × $6.50 = $260.
- Volume: 40 ÷ 12 = 3.3 cubic feet; at about 45 lb per cubic foot, the load weighs roughly 150 lb.
Board feet of common sizes
| Board | Board feet per 8 ft | Board feet per 12 ft |
|---|---|---|
| 1 × 6 | 4.0 | 6.0 |
| 2 × 4 | 5.3 | 8.0 |
| 2 × 6 | 8.0 | 12.0 |
| 2 × 10 | 13.3 | 20.0 |
| 4 × 4 | 10.7 | 16.0 |
Tips for buying by the board foot
- Allow for waste. Rough lumber loses thickness and width when planed and jointed, and defects get cut out. Add 20 to 30% for furniture projects.
- Check the grade. FAS (firsts and seconds) gives long clear pieces; No. 1 Common is cheaper but yields shorter clear sections.
- Moisture matters. Kiln-dried hardwood at 6 to 8% moisture is stable for furniture. Green wood is heavier and will shrink.
- Weight varies by species. Spruce-pine-fir is about 28 lb per cubic foot, red oak and maple about 44 to 45 lb, so a truckload of oak weighs much more than the same volume of framing lumber.