Lumber Board Feet Calculator
Compute the board footage of a lumber piece from thickness, width, and length so you can price and order materials accurately. Useful for woodworking, framing, and hardwood purchasing.
Last updated: May 2026
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About this calculator
A board foot (bf) is the standard volume unit for pricing dimensional and rough-sawn lumber in North America: 1 board foot = 144 cubic inches, equivalent to a piece 1 inch thick × 12 inches wide × 12 inches long. The formula is BF = (T × W × L) / 12, where T is thickness in inches, W is width in inches, and L is length in feet (not inches). The /12 handles the mixed units: multiplying L (feet) by 12 converts it to inches, then dividing the cubic-inch product by 144 (cubic inches per board foot) is the same as dividing the inch × inch × foot product by 12 directly. Variables: thickness usually ranges from 1/2 inch (½-inch dimensional) to 8/4 inches and beyond for rough lumber, width from 2 to 12+ inches, and length from 6 to 16 feet. Edge cases: hardwood lumber yards typically use nominal-thickness pricing called 'quarter' grading — 4/4 = 1 inch, 5/4 = 1.25 inch, 8/4 = 2 inch — and round the thickness up to the next quarter for billing even if the actual thickness is slightly less. Softwood dimensional lumber (2×4, 2×6) uses nominal dimensions that are smaller than actual: a '2×4' is actually 1½ × 3½ inches; if you compute board feet using nominal dimensions you slightly overstate the actual wood volume, but this is the convention used in pricing. Surfaced (S2S, S4S) lumber is typically priced on the rough size before surfacing. Always verify which convention your supplier uses. Waste allowances: for hardwoods buy 15–25% over net required (cutting around defects, planing); for clean softwood dimensional lumber 10% is usually sufficient.
How to use
Example 1 — hardwood plank. A piece 4/4 (1 inch) thick, 6 inches wide, and 8 feet long. BF = (T_in × W_in × L_ft) / 12 = (1 × 6 × 8) / 12 = 48 / 12 = 4 bf. Check against the definition: 1 × 6 × 96 in = 576 cu in, and 576 / 144 cu in per board foot = 4 bf — matches. At $8/bf, this plank costs 4 × $8 = $32. Example 2 — 12-piece order. Twelve 2 in × 4 in × 8 ft framing studs. Per piece: (2 × 4 × 8) / 12 = 64 / 12 = 5.33 bf. Twelve pieces: 12 × 5.33 = 64 bf. At $1.20/bf: 64 × $1.20 = $76.80 total. Check: each stud is 2 × 4 × 96 = 768 cu in; 768 / 144 = 5.33 bf — matches.
Frequently asked questions
What is the difference between a board foot and a linear foot when buying lumber?
A board foot is a volume measurement (144 cubic inches), while a linear foot is a length measurement with no regard for thickness or width. Dimensional softwood lumber like 2×4 studs is typically sold per linear foot or per piece because every piece has standardized dimensions — you only need to specify length. Hardwood lumber and rough-cut stock is sold by the board foot because thickness and width vary piece by piece, and pricing must scale with the volume of wood you take home. Some specialty woods (figured maple, quartersawn oak) carry premium per-bf pricing that can be 5–10× standard species. When comparing prices, always confirm the unit — buying '$5 per foot' lumber sight-unseen could mean per linear foot or per board foot, a 4–6× difference in actual cost.
How do hardwood thickness gradings (4/4, 5/4, 8/4) work for board-feet calculations?
Hardwood lumber is sold in 'quarter' increments where the numerator counts quarter-inch units: 4/4 = 1 inch, 5/4 = 1.25 inch, 6/4 = 1.5 inch, 8/4 = 2 inch, 12/4 = 3 inch, 16/4 = 4 inch. The board-foot calculation uses the nominal thickness, not the surfaced thickness. A 4/4 board surfaced on two sides (S2S) typically ends up about 13/16 inch thick, but it is still priced as 1-inch (4/4) stock. For grading purposes, lumber dealers round actual thickness up to the next quarter — a board measuring 7/8 inch may be sold as 4/4. Plug the nominal thickness into the formula: a 5/4 board 6 inches wide and 8 feet long is (1.25 × 6 × 8)/12 = 5 bf. When ordering thicker hardwood (8/4 and above), expect 10–20% premium over thinner stock per board foot due to drying difficulty and lower kiln yield.
How much waste should I add when ordering lumber by board feet for a project?
Waste percentages depend heavily on material and project type. For straight-cut, defect-free dimensional softwood (framing 2×4, 2×6), add 10% over net needs to cover end-trims and the occasional defective stick. For hardwood furniture-grade lumber, add 15–25% because you will cut around knots, splits, end-checking, and grain-orientation choices. For figured or quartersawn wood where you need specific grain direction, add 30–40%. Projects with many small parts (cabinet doors, small turning blanks) generate more waste than projects with long, simple cuts. Curved work (bent laminations, sculpted parts) can waste 50–70% of starting stock. Add an extra 5–10% on top of any of these for first-time use of unfamiliar wood, since you cannot predict your defect rate. It is generally cheaper to over-order initially than to make a second trip or wait for a reorder mid-project.
What are common mistakes when calculating board feet?
The most frequent mistake is mixing units in the formula — entering length in inches instead of feet, which produces a result 12× too small. Always check that thickness and width are in inches but length is in feet (the /144 in the standard formula assumes this). Another common error is using actual surfaced dimensions instead of nominal sizes; a '2×4' is nominally 2×4 for pricing but actually 1.5×3.5 inches, so using actual dims understates board feet on softwood. Forgetting to round up at the hardwood yard — many dealers bill at the next-quarter thickness even if actual measurement is less — leads to budgeting surprises. People also assume rough lumber and surfaced lumber are interchangeable; rough lumber is cheaper per board foot but requires planing and jointing that can reduce final thickness by 20% and lose 5–10% of width to straightening. Finally, computing volume (in cubic inches) and treating that number as board feet directly loses the /144 conversion and overstates volume by 144×.
When should I NOT use this calculator?
Skip board-feet calculations for plywood, OSB, MDF, particleboard, and other sheet goods — these are priced per sheet or per square foot, not by board feet. Do not use it for veneer or thin-stock applications where pricing is per square foot of face area regardless of thickness. Avoid it for international wood-product pricing in countries that use cubic meters or board measure (Hoppus feet in some Commonwealth markets) — those need different conversion factors. The formula is also inappropriate for log-scale pricing of standing or felled timber, where Doyle, Scribner, or International ¼-inch log rules apply and account for losses during sawing. For high-end exotic hardwoods sold by weight (lignum vitae, snakewood), board feet may be a secondary measure to mass. Finally, if you are ordering finished components (mouldings, doors, cabinet panels) that are priced by linear foot or per piece, the board-foot framework is irrelevant — use the supplier's specified unit.