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Board Foot Calculator
Calculate board feet - the standard US lumber volume unit - plus a waste allowance and total lumber cost.
A board foot is the standard unit lumber is bought and sold by in the US: one board foot equals a piece of wood 12 inches long, 12 inches wide and 1 inch thick - 144 cubic inches of wood. Enter a board's thickness, width, length and how many identical boards you need, and this calculator returns the board footage - plus, since that's rarely the last step in pricing out a lumber order, an optional waste allowance and a total cost from a price per board foot. Lumber pricing and yield calculations both use the board's nominal dimensions (the size it's labeled and sold as, like a "2×4"), not its smaller actual size after drying and planing - see the reference table below for common nominal-to-actual conversions.
T · Nominal thickness of the board, e.g. 2 for a 2×4.
W · Nominal width of the board, e.g. 4 for a 2×4.
L · Length of the board.
Qty · Number of identical boards being calculated.
Waste & Cost (Optional)
W% · Commonly 10-20% for cutting waste and defects
$ · Leave blank to skip cost estimate
Solution
Enter the board dimensions and quantity to calculate board feet.
BF = T(in) × W(in) × L(ft) / 12
Formula Sheet
- BFBoard Feet
- TThickness
- WWidth
- LLength
- QtyQuantity
- W%Waste Factor
Variables & Units
| Symbol | Variable | Description | Common Units |
|---|---|---|---|
| BF | Board Feet | Lumber volume, the standard US unit for buying and selling wood. | bd ft, ft³ |
| T | Thickness | Nominal thickness of the board, e.g. 2 for a 2×4. | mm, cm, m, in, ft |
| W | Width | Nominal width of the board, e.g. 4 for a 2×4. | mm, cm, m, in, ft |
| L | Length | Length of the board. | mm, cm, m, in, ft |
| Qty | Quantity | Number of identical boards being calculated. | |
| W% | Waste Factor | A decimal allowance for cutting waste, defects, and warped stock (e.g. 0.10 = 10%). |
How to Use This Calculator
- 01Enter the board's thickness and width - for standard lumber, use the nominal size printed on the label (e.g. 2 and 4 for a "2×4"), not the smaller actual dressed size.
- 02Enter the board's length.
- 03Enter how many identical boards you're calculating for - leave it at 1 for a single board.
- 04Optionally set a Waste Factor (commonly 10-20%) to cover cutting waste, knots, and warped stock, and a Price per Board Foot for a total cost estimate.
- 05Select Calculate to see the board footage per board, the total for the full quantity, and - if a price was entered - the total cost.
How the Formula Works
A board foot measures volume, not just length: Board Feet = Thickness(in) × Width(in) × Length(ft) / 12. The division by 12 exists because thickness and width are measured in inches while length is measured in feet - mixing those two units in one formula is unusual, but it's the standard convention because a board foot itself is defined from a 1-inch-thick, 1-foot-square board.
Lumber has been priced and measured by the board foot since well before modern dimensional lumber was dried and planed to a smaller finished size, and the industry never switched - a board sold as a "2×4" is billed using the nominal 2 inches × 4 inches figure even though it actually measures about 1.5 × 3.5 inches once dried and surfaced. This calculator follows that same convention: enter the nominal size printed on the lumber, not its measured actual size, to get the board footage a lumberyard would quote.
Worked Example 01
Board feet for a single rough board
Known
- Thickness (T): 1 in
- Width (W): 12 in
- Length (L): 1 ft
- Quantity: 1
Formula
BF = T(in) × W(in) × L(ft) / 12
Substitution
BF = 1 × 12 × 1 / 12
Result
BF = 1 bd ft
This is the textbook definition of a board foot itself - a board 1 inch thick, 12 inches wide and 1 foot long is exactly 1 board foot.
Worked Example 02
Board feet for a common dimensional board
Known
- Thickness (T): 2 in
- Width (W): 4 in
- Length (L): 10 ft
- Quantity: 1
Formula
BF = T(in) × W(in) × L(ft) / 12
Substitution
BF = 2 × 4 × 10 / 12
Result
BF = 6.6667 bd ft
A single 2×4 that's 10 feet long comes to about 6.67 board feet - this is the nominal-size figure a lumberyard would use to price it.
Worked Example 03
Total board feet for multiple boards
Known
- Thickness (T): 2 in
- Width (W): 6 in
- Length (L): 8 ft
- Quantity: 5
Formula
BF = T(in) × W(in) × L(ft) / 12
Substitution
BF = (2 × 6 × 8 / 12) × 5
Result
BF = 40 bd ft
Five 2×6 boards, each 8 feet long, come to 8 board feet apiece - 40 board feet in total for the order.
Worked Example 04
Total cost with a waste allowance
Known
- Thickness (T): 2 in
- Width (W): 6 in
- Length (L): 8 ft
- Quantity: 5
- Waste Factor (W%): 10%
- Price per Board Foot: $3.00
Formula
Cost = BF (with waste) × Price per Board Foot
Substitution
BF = 40, BF (with waste) = 40 × 1.10 = 44, Cost = 44 × 3
Result
44 bd ft to purchase · $132.00
The same five 2×6 boards from the previous example come to 40 raw board feet, but with a 10% waste allowance for cutting and defects, that's 44 board feet to actually purchase - at $3.00 per board foot, a total cost of $132.00.
Applications
- 01Estimating the total lumber volume, and therefore cost, needed for a woodworking or framing project
- 02Comparing lumber prices quoted per board foot across different suppliers or wood species
- 03Converting a cut list of board dimensions into a single purchasing quantity
Nominal vs. Actual Lumber Dimensions
| Nominal Size | Actual Size (in) |
|---|---|
| 1×4 | 0.75 × 3.5 |
| 1×6 | 0.75 × 5.5 |
| 1×8 | 0.75 × 7.25 |
| 2×4 | 1.5 × 3.5 |
| 2×6 | 1.5 × 5.5 |
| 2×8 | 1.5 × 7.25 |
| 2×10 | 1.5 × 9.25 |
| 2×12 | 1.5 × 11.25 |
Assumptions
- 01Thickness and width are entered as nominal lumber dimensions (the labeled size), matching standard lumberyard pricing convention, not the smaller actual dressed size.
- 02All boards in the quantity are identical in thickness, width and length.
- 03The board is a simple rectangular prism - irregular shapes, tapers, and waste from cutting are not accounted for beyond the optional waste factor.
Where This Model Stops
- 01Waste factor is a single flat percentage applied to the total board footage - it doesn't model a specific cut list or which individual boards are more likely to have defects.
- 02Cost is based on a single flat price per board foot - it doesn't model grade-based, length-based, or quantity-discount pricing some suppliers use.
- 03Not applicable to sheet goods (plywood, MDF) sold by square footage rather than board footage, or to lumber grades sold by the linear foot.
- 04Rough-sawn, surfaced, quarter-sawn, live-edge, and specialty hardwood stock can be sold with supplier-specific measurement rules. Use the seller's stated convention for an invoice-level estimate.
References
- [1]
Board foot
Standard US lumber industry measurement convention
1 board foot = 144 cubic inches = a 12in × 12in × 1in board. BF = T(in) × W(in) × L(ft) / 12.
Frequently Asked Questions
Why does the formula divide by 12 instead of 144?
Both give the same answer. Dividing thickness(in) × width(in) × length(ft) by 12 is the standard lumber-industry shorthand; the equivalent "pure volume" version converts length to inches too and divides the whole cubic-inch volume by 144, since a board foot equals 144 cubic inches. This calculator computes internally using the 144 cubic-inch definition so it works correctly regardless of which units you pick, and displays the familiar 12-based formula since that's what most lumber references use.
Should I use nominal or actual lumber dimensions?
Use nominal - the size printed on the label, like the 2 and 4 in "2×4" - not the smaller size you'd get from measuring the board with a tape measure. Board-foot pricing has always been based on nominal size, even though dried and planed lumber is measurably smaller.
How much waste allowance should I add?
10-20% is the commonly cited range - closer to 10% for straightforward cuts from clean stock, closer to 20% for a complex cut list, lower-grade lumber with more knots and defects, or boards prone to warping. Leave the Waste Factor field blank (or 0) to see the raw board footage of the boards themselves with no allowance added.
Does the cost use the raw board footage or the waste-adjusted total?
The waste-adjusted total - cost is meant to reflect what you'd actually pay for the lumber you need to purchase, including the waste allowance, not just the theoretical board footage of the finished boards themselves.
Can I use this to challenge a lumberyard invoice?
Use it as a sanity check, not a final billing authority. Lumberyards may quote nominal dimensions, minimum billed widths, rough-sawn rules, or board-foot rounding policies that differ by species, grade, and supplier.