Board Foot Calculator — Lumber Volume & Cost
Calculate board feet, total volume, and cost for any lumber order. Enter length, width, thickness, and quantity — the calculator handles nominal or actual sizing in either unit system.
Board Foot Calculator
Nominal vs Actual Lumber Sizes
Construction lumber is sold by nominal size (the rough-cut dimension), but the actual finished size is smaller because the board is dried and planed. Both work in the formula — just be consistent.
| Nominal | Actual (in) | Actual (mm) | BF per ft of length |
|---|---|---|---|
| 1×4 | 0.75 × 3.5 | 19 × 89 | 0.33 (nom) / 0.219 (act) |
| 1×6 | 0.75 × 5.5 | 19 × 140 | 0.50 (nom) / 0.344 (act) |
| 2×4 | 1.5 × 3.5 | 38 × 89 | 0.667 (nom) / 0.438 (act) |
| 2×6 | 1.5 × 5.5 | 38 × 140 | 1.0 (nom) / 0.688 (act) |
| 2×8 | 1.5 × 7.25 | 38 × 184 | 1.33 (nom) / 0.906 (act) |
| 2×10 | 1.5 × 9.25 | 38 × 235 | 1.67 (nom) / 1.156 (act) |
| 2×12 | 1.5 × 11.25 | 38 × 286 | 2.0 (nom) / 1.406 (act) |
| 4×4 | 3.5 × 3.5 | 89 × 89 | 1.33 (nom) / 1.021 (act) |
How to Calculate Board Feet
The board foot formula is straightforward, but pay attention to which dimensions are in feet vs inches.
Formula: BF = (Lengthft × Widthin × Thicknessin) ÷ 12
- Convert length to feet, but keep width and thickness in inches.
- Multiply the three numbers.
- Divide by 12 (since 1 BF = 1 ft × 12 in × 1 in ÷ 12).
- Multiply by the number of pieces.
Imperial example: 10 pieces of 2×6×8 ft (nominal): per piece = (8 × 6 × 2) ÷ 12 = 8 BF. Total = 10 × 8 = 80 BF. At $3.50/BF = $280.
Metric example: 10 pieces of 2.4 m × 15 cm × 5 cm. Convert: 2.4 m = 7.87 ft, 15 cm = 5.91 in, 5 cm = 1.97 in. BF per piece = (7.87 × 5.91 × 1.97) ÷ 12 = 7.64 BF. Total = 76.4 BF.
Quarter Sizing (Hardwood Convention)
Hardwood lumber thickness is sold in quarter-inch increments: 4/4 = 1″, 5/4 = 1.25″, 6/4 = 1.5″, 8/4 = 2″, etc. The number is the thickness in quarter inches, before drying and planing. After surfacing (S2S = surfaced two sides), the actual thickness is typically 1/4 inch less than nominal.
- 4/4 (1″ nominal): 13/16″ actual after S2S — most common for furniture and trim.
- 5/4 (1¼″ nominal): ~1″ actual — common for stair treads and shelves.
- 6/4 (1½″ nominal): ~1¼″ actual — table tops, heavier work.
- 8/4 (2″ nominal): ~1¾″ actual — chair legs, bench tops.
Typical Lumber Cost per Board Foot
| Species / Type | Price per BF | Notes |
|---|---|---|
| SPF (Spruce-Pine-Fir, construction) | $2–$5 | Studs, framing, basic projects |
| Pressure-treated pine | $3–$7 | Outdoor, decks, fences |
| Cedar | $4–$8 | Outdoor furniture, siding |
| Poplar | $4–$7 | Paint-grade trim, drawer sides |
| Red oak | $5–$9 | Furniture, flooring, cabinets |
| Hard maple | $7–$12 | Tabletops, butcher blocks |
| Walnut | $12–$25 | Premium furniture, accents |
| Cherry | $10–$18 | Cabinetry, fine furniture |
2026 US averages. Custom mills, FAS-grade, or wide planks command 20–50% premiums. Prices fluctuate with supply.
Frequently Asked Questions
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches — a piece 12″ long, 12″ wide, and 1″ thick. Lumber yards price most rough hardwoods and bulk softwoods by the board foot. Formula: BF = (length in feet × width in inches × thickness in inches) ÷ 12.
How many board feet in a 2×4×8?
A nominal 2×4×8 (8 ft long) is 5.33 board feet using nominal dimensions: (8 × 4 × 2) ÷ 12 = 5.33 BF. Using actual dimensions (1.5×3.5 in), it’s 3.5 BF. Lumber is typically sold and quoted using nominal sizing.
What is the difference between nominal and actual lumber size?
Nominal is the rough-cut name (2×4) before drying and surfacing. Actual is what you measure (1.5×3.5 in / 38×89 mm) after the board is planed. For board-foot calculations, use whichever the supplier specifies — most retail lumber is priced on nominal, while custom hardwoods may use actual.
How much does lumber cost per board foot?
$2–$5 per BF for standard SPF (spruce-pine-fir) construction lumber. $4–$8 for cedar or pressure-treated. $6–$15 for common hardwoods (oak, maple, poplar). $20+ for premium hardwoods (walnut, cherry, exotic species). Prices vary widely by region and grade.
Related Calculators
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- Cubic Yards Calculator — generic volume math
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- Decking Calculator — building a deck? Get the full materials list
- Stair Calculator — lumber for stair stringers and treads
- Fence Calculator — lumber for fence posts and rails
- All Construction Calculators
Board foot is a US-standard volume unit for lumber. Outside the US, lumber is typically sold by the linear meter or by the cubic meter (1 m³ ≈ 423.776 BF). Always confirm sizing convention (nominal vs actual) with your supplier.
