Board feet explained (simple formula and examples)

The board foot formula

Board feet measure volume. A common formula is: board feet = (thickness in inches × width in inches × length in feet) / 12.

Example

A 2×6 that is 8 feet long is: (2 × 6 × 8) / 12 = 8 board feet (using nominal dimensions). If you are buying surfaced lumber, remember actual thickness/width can be smaller.

Common mistakes

• Mixing nominal and actual sizes without noticing.
• Forgetting to convert inches/feet consistently.
• Not planning extra for defects, cutoffs, and grain matching.

Surfacing and kerf (why rough vs finished matters)

Rough-sawn lumber is thicker and wider than the finished size after surfacing. Plan your board feet based on the rough size you are buying, then confirm the finished thickness you need (S2S/S3S/S4S).

• Plan extra if you need to plane or joint boards heavily.
• Saw kerf (the blade cut) reduces usable length on repeated cuts.

Nominal vs actual size (why it changes board feet)

Many softwood boards are sold by nominal size (2×6, 2×4), but the actual dressed size is smaller. If you price by board feet, be clear about which size you’re using.

Hardwood thickness terms (4/4, 5/4, 8/4)

Hardwoods are often priced using “quarters” for thickness: 4/4 is about 1 inch rough thickness, 5/4 is about 1.25 inches, and 8/4 is about 2 inches. After surfacing, the finished thickness is typically less.

• If you’re matching an existing piece, ask for the finished thickness (S2S/S3S/S4S) before you calculate board feet.
• Wide boards and long lengths can be limited by stock availability, so ordering extra can avoid project delays.

Moisture and movement (planning for wood movement)

• Wood moves with humidity; acclimate lumber if the project requires stable dimensions.
• Outdoor projects need species-appropriate treatment and fasteners.
• If you are matching an existing floor or trim, moisture content matters as much as size.

How to estimate lumber for a project (simple workflow)

• List parts by thickness × width × length and quantity (cut list).
• Convert each part to board feet and sum the total.
• Add waste allowance based on the project: straight framing can be lower; furniture-grade and grain-matching can be higher.
• If the lumberyard charges by linear foot for certain products (trim, decking, studs), compare both pricing methods to avoid surprises.

Grade and yield (why you might need more)

• Lower grades have more knots and defects, which reduce usable yield.
• If you need clear or long pieces, plan extra board feet for selection.
• Ask your supplier about minimum length rules and width upcharges.

Waste allowance tips (avoid running short)

• Knots, checks, and warping reduce usable yield (especially in wide boards).
• Mitered trim and angled cuts increase offcuts that can’t be reused.
• If boards must be color/grain matched, you often need more extra to select pieces.

Pricing example (turn board feet into cost)

If hardwood is priced at $7.50 per board foot and your project needs 28 board feet, the rough material cost is 28 × 7.50 = $210 (before waste allowance, tax, delivery, and surfacing charges).

If the lumberyard applies a minimum length, width upcharge, or surfacing fee, include those items separately; they can be significant for small projects.

Board foot vs linear foot (avoid a common confusion)

• Trim and some decking products are priced by linear foot; hardwood and many rough boards are priced by board foot.
• A board-foot calculation needs thickness, width, and length. A linear-foot price usually assumes a standard profile/size.
• If you’re comparing two quotes, confirm they’re using the same unit and the same dimensions (nominal vs actual).

• Board feet calculator
• Deck board calculator