What a board foot is
A board foot is a unit of lumber volume: a piece 1 in thick, 12 in wide and 12 in long, or 144 cubic inches. Hardwood dealers and sawmills typically price lumber by the board foot, while home centers usually price dimensional softwood like 2×4s by the piece. Knowing board feet lets you compare prices and estimate a project budget.
How to measure
- Thickness in inches. Rough hardwood is sold in quarters: 4/4 is 1 in, 5/4 is 1.25 in, 6/4 is 1.5 in and 8/4 is 2 in. Many dealers figure board feet from this rough thickness even after surfacing. Ask how your yard measures.
- Width in inches. Measure the actual width. Random-width hardwood varies board to board.
- Length in feet. Measure the full board length.
The formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12, times the number of boards. Enter a price per board foot to estimate cost.
Worked example
You are buying five boards of 8/4 walnut, each 7 in wide and 8 ft long:
- One board: 2 × 7 × 8 ÷ 12 = 9.33 board feet
- Five boards: 46.67 board feet
- If the yard charges $12 per board foot, that is about $560
A second example: a 2×4 that is 8 ft long is 2 × 4 × 8 ÷ 12 = 5.33 board feet using nominal size, even though its actual dimensions are about 1.5 × 3.5 in.
Planning a project and waste
Work out the board feet in your cut list (every finished part), then add extra for defects, knots, checks at board ends, saw kerf and grain matching. Woodworkers commonly add roughly 20–30% for hardwood projects, and more for figured wood or when matching color and grain matters. Rough lumber also loses thickness and width when it is jointed and planed.
Common mistakes
- Mixing nominal and actual sizes. Softwood dimensional lumber is sold by nominal size; hardwood is often figured from rough thickness. Know which your dealer uses before comparing prices.
- Measuring length in inches. The length box is in feet.
- Forgetting milling loss. A rough 4/4 board usually surfaces to around ¾ in or a bit more, so plan thickness accordingly.
- Skipping the moisture check. Wood that is too wet for indoor use can shrink, cup or crack after you build. A moisture meter helps, and letting lumber acclimate in your shop before milling is common practice.
Buying tips
- Hardwood dealers often grade lumber (for example FAS or Select and #1 Common). Higher grades give longer clear cuttings; lower grades can be a good value for small parts.
- S2S means surfaced on two sides, S4S means all four sides, and rough means unsurfaced. Rough is usually cheaper per board foot but needs a jointer and planer.
- Bring your cut list and a tape measure, and pick boards that fit your parts with the least waste.
- Store lumber flat and stickered (with spacers between layers) so air can circulate.
Check lumber before building