Board Foot Calculator
Calculate board feet for lumber. Essential for buying hardwood lumber and determining material costs for woodworking projects.
Reviewed by the Calcura editorial team · Last reviewed
- Question
- How do I calculate board feet for lumber?
- Answer
- board_feet = (T_in × W_in × L_ft) / 12, where thickness and width are in inches, length is in feet. A 4/4 (1") × 6" × 8' board = (1 × 6 × 8) / 12 = 4 board feet. One board foot equals 144 cubic inches (1 × 12 × 12). Multiply by the count of boards, then by the per-board-foot price for the total cost.
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- Formula
bf = (T_in × W_in × L_ft) / 12- Caveats
- Hardwood is priced in board feet; dimensional softwood (2×4, etc.) is priced by the piece.
- Rough-sawn lumber uses nominal thickness (4/4 = 1" nominal, ~13/16" surfaced); use actual measurements.
- Always buy 20–30% extra — warp, defects, and mis-cuts eat into the calculated yield.
What This Calculator Does
Calculates the volume of a lumber order in board feet — the standard US hardwood pricing unit where 1 board foot = 144 cubic inches (1 in × 12 in × 12 in). Multiplies across pieces and converts to cubic feet or cubic meters for metric suppliers. Works for rough or S4S (surfaced four sides) lumber as long as you use the actual measured dimensions.
When To Use This Calculator
Buying hardwood for a furniture build
Six 4/4 oak boards, 6" × 8': (1 × 6 × 8) / 12 × 6 = 24 board feet. At $6/bf = $144 before tax.
Comparing a per-bf quote against a per-piece price
A lumberyard quotes $42 for a 1×8×10 walnut board. 6.67 bf → $6.30/bf — check against the posted $7/bf rate.
Estimating cubic-meter volume for a metric supplier
Ten 25 mm × 150 mm × 2.4 m boards: 0.025 × 0.15 × 2.4 × 10 = 0.09 m³.
Converting between thickness grades (4/4, 5/4, 8/4)
Hardwood is priced by rough thickness. A 4/4 order billed as 1" even after planing to 3/4" — the calculator uses the rough dimension.
How It Works
A board foot is 144 cubic inches of wood. The familiar formula (T × W × L) / 12 works because thickness and width are entered in inches and length in feet — multiplying feet by 12 internally converts length to inches, and the result is cubic inches ÷ 144. Hardwood yards sell by this volume regardless of board shape, so a tapered or narrow board still contributes its full volumetric share. For metric inputs (cm × cm × m), the calculator converts dimensions to inches/feet first so the board-foot number matches what a US supplier would bill. Nominal softwood sizes (2×4 = 1.5 × 3.5 actual) must be entered at actual dimensions, not nominal.
Formula
board_feet = (thickness_in × width_in × length_ft) / 12 | cubic_feet = board_feet / 12 | cubic_meters = (thickness_cm/100) × (width_cm/100) × length_mReal-World Example
Scenario
A small dining table needs a top made from four 4/4 cherry boards, each 6 inches wide and 6 feet long, plus four 8/4 cherry legs at 3 inches square and 29 inches long. Cherry runs $8/bf at the local yard. Add 15% waste.
Calculation
Top: (1 × 6 × 6) / 12 × 4 = 12 bf. Legs: (2 × 3 × 29/12) / 12 × 4 = 4.83 bf. Total = 16.83 bf. With 15% waste: 16.83 × 1.15 = 19.35 bf. Cost: 19.35 × $8 = $154.80.
Result
Buy ~20 board feet of 4/4 and 8/4 cherry — roughly $155 in lumber before tax and any defects on the shelf.
Common Mistakes to Avoid
Mistake: Using nominal softwood dimensions in the formula
Solution: A 2×4 is actually 1.5×3.5 inches after planing. Plug in 1.5 and 3.5, not 2 and 4, or you'll overestimate volume by ~23%.
Mistake: Forgetting to add waste for cuts and defect rejection
Solution: Rough hardwood has checks, knots, and end splits. Add 15% for straightforward cuts, 20–30% for grain-matching or curved pieces.
Mistake: Confusing board feet with linear feet
Solution: Linear feet ignore thickness and width. A 2×12 at 8 ft is 16 bf but only 8 linear ft. Hardwood almost always sells by bf.
Mistake: Using planed (S4S) dimensions for hardwood priced as 4/4, 5/4, etc.
Solution: Hardwood is billed at rough (pre-planing) thickness. 4/4 stock is billed as 1" even though it planes to ~13/16". Enter the rough dimension.
Related DIY tools
Concrete Volume Calculator
Move from board feet for framing to cubic yards of concrete for the slab underneath.
Fence Calculator
Estimate posts, rails, and pickets in linear feet rather than board feet.
Paint Coverage Calculator
Finish the built lumber — compute gallons of stain or sealer by surface area.
When This Isn't the Right Tool
Sheet goods (plywood, MDF, OSB)
Use instead: Sheet goods are priced by the sheet or per square foot, not board feet. Use area × sheet count.
Round or tapered turning blanks
Use instead: Turning stock is usually sold by piece or weight. Board-foot math on a cylinder overstates the price by ~21% (π/4 fill).
Decking and dimensional softwood priced per piece
Use instead: Big-box 2× stock is sold by the board — price depends on length, not volume. Use the sticker price, not bf.
How to Verify This Calculation
Sanity checks: 1" × 12" × 12 ft = 12 bf exactly. 1" × 6" × 8 ft = 4 bf exactly. 2" × 6" × 12 ft = 12 bf. Any deviation means thickness was entered in feet or length was entered in inches.
Sources
- NIST Handbook 44 — lumber measurement standards — Authoritative US reference defining the board foot unit.
- National Hardwood Lumber Association — grading rules and measurement — Industry standard for hardwood sizing (4/4, 5/4, 8/4) and tally-by-the-board-foot pricing.
- American Softwood Lumber Standard (PS 20) — Defines nominal vs actual dimensions for 2×4, 2×6, and other construction lumber.
- BIPM — SI Brochure — Basis for the cubic-meter metric conversion (1 in = 2.54 cm exact).
Reviewed by the Calcura editorial team · Last reviewed