Board Foot Calculator: Lumber Formula (T×W×L)/12 Explained
A board foot calculator answers the question lumber buyers ask every day: how much wood is in this board, and what will it cost at $X per BF? Use a free board foot calculator to convert thickness, width, and length into board feet before you fill the truck.
Below is the standard formula, unit rules, and examples that match how yards and sawmills quote hardwood and softwood.
Estimate lumber volume in board feet
Free board foot calculator — thickness, width, length to BF in seconds.
Board Feet Formula: (T × W × L) ÷ 12
One board foot is 144 cubic inches of wood. The everyday shop formula uses thickness and width in inches and length in feet:
Where T = thickness (in), W = width (in), L = length (ft). If length is also in inches:
Example: A 1″ × 8″ × 10 ft board.
- (1 × 8 × 10) ÷ 12 = 80 ÷ 12
- Result: 6.67 board feet
- At $6.50/BF, cost ≈ $43.33 before tax
Thickness, Width, and Length Units
Mixing units is the #1 source of wrong BF totals. Keep this checklist consistent:
Unit checklist
- Thickness: inches (use 0.75 for 3/4″ plywood; 4/4 hardwood ≈ 1″ rough)
- Width: inches (measure actual face width for random-width stock)
- Length: feet in the ÷12 formula (convert 96″ → 8 ft)
- Multiply by quantity for stacks: BF per board × number of boards
Nominal vs Actual Size When Buying Lumber
A “2×4” is not 2″ × 4″ after surfacing. Yards often price construction lumber and hardwood on nominal or seller rules, while project takeoffs may use actual dressed sizes. Always confirm which convention your quote uses.
- 2×4×8 nominal: (2 × 4 × 8) ÷ 12 = 5.33 BF
- Same board actual (~1.5×3.5×8): (1.5 × 3.5 × 8) ÷ 12 = 3.5 BF
- Hardwood “4/4” is roughly 1″ rough; S2S/S4S will be thinner — measure if accuracy matters.
Practical Buying Tips
Add waste for defects, grain matching, and cutoffs — often 10–20% for furniture-grade hardwood. Price = total BF × $/BF, then compare species and grade, not just the sticker length.
Run each stick or cut list through the ToolMars board foot calculator so your estimate matches the invoice math.
Estimate lumber volume in board feet
Free board foot calculator — thickness, width, length to BF in seconds.
Frequently Asked Questions
What is a board foot?
A volume of wood equal to 1″ × 12″ × 12″ (144 cubic inches), used to price lumber.
How do you calculate board feet?
(Thickness in × Width in × Length ft) ÷ 12. Or (T × W × L in inches) ÷ 144.
Do you use nominal or actual thickness for board feet?
Suppliers often price on nominal size; project math may use actual dimensions — ask which applies.
How many board feet are in a 2×4×8?
About 5.33 BF nominal, or 3.5 BF using typical actual 1.5″ × 3.5″ dimensions.
Is a board foot the same as a linear foot?
No — linear feet are length only; board feet measure volume.