Lumber yards count boards one way and price them another: you bring a list of pieces, a hardwood dealer answers in board feet.
Get the conversion wrong and the gap is not small. Plug actual framing sizes into a yard’s nominal-size price and you undercount by about a third. Divide inches by 12 instead of 144 and the answer is twelve times too big.
Knowing how to calculate board feet the way the yard does avoids both, and the board foot calculator runs it for a whole list at once.
What is a board foot?
A board foot is a unit of wood volume, not length or area. It equals 144 cubic inches: a board 1 inch thick, 12 inches wide and 12 inches long.
The American Hardwood Export Council uses the same definition and the same working formula: width in inches times length in feet times thickness in inches, divided by 12 (AHEC, checked November 2026).
Very different shapes can hold the same volume. Each of these is exactly one board foot:
| Board | Calculation | Board feet |
|---|---|---|
| 1 in thick, 12 in wide, 1 ft long | 1 × 12 × 1 ÷ 12 | 1 |
| 2 in thick, 6 in wide, 1 ft long | 2 × 6 × 1 ÷ 12 | 1 |
| 1 in thick, 4 in wide, 3 ft long | 1 × 4 × 3 ÷ 12 | 1 |
That is why board feet compare boards fairly where a count of pieces cannot. It is the first thing to grasp about how to calculate board feet: you are measuring volume.
How to calculate board feet, step by step
- Measure the board in the units the seller uses. Thickness and width in inches, length in feet. For framing lumber that means the nominal size on the tag; for hardwood, the thickness in quarters.
- Multiply the three numbers. Thickness × width × length.
- Divide by 12. That is board feet for one piece. Multiply by the number of pieces for the line total.
Board feet = Thickness × Width × Length ÷ 12
Both versions agree. A 2x6 that is 8 feet long is 2 × 6 × 8 ÷ 12 = 8 board feet; with the length as 96 inches it is 2 × 6 × 96 ÷ 144 = 8 again.
Board feet per piece for common framing sizes
This chart answers common questions, such as how many board feet are in a 2x4x8 or a 2x6x10. Values use nominal sizes, the basis board feet are figured on.
| Size | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 2x4 | 5.33 | 6.67 | 8 | 10.67 |
| 2x6 | 8 | 10 | 12 | 16 |
| 2x8 | 10.67 | 13.33 | 16 | 21.33 |
| 2x10 | 13.33 | 16.67 | 20 | 26.67 |
| 2x12 | 16 | 20 | 24 | 32 |
| 4x4 | 10.67 | 13.33 | 16 | 21.33 |
Shortcut: a 2x6 holds exactly 1 board foot per foot, so its board footage equals its length in feet. More framing tools: framing and carpentry calculators.
A worked example: board feet for a whole cut list
Real projects mix sizes, and knowing how to calculate board feet for a mixed list is where a tidy list saves money. Here is a red oak bookcase, figured the way a hardwood dealer would.
| Part | Pieces | Thickness | Width | Length | Board feet |
|---|---|---|---|---|---|
| Sides | 2 | 4/4 (1 in) | 12 in | 6 ft | 12 |
| Shelves | 5 | 4/4 (1 in) | 10 in | 3 ft | 12.5 |
| Base and top rails | 2 | 8/4 (2 in) | 4 in | 3 ft | 4 |
| Total | 28.5 |
Add a 15% allowance for knots, checks and saw cuts in rough hardwood (your allowance depends on the grade you buy):
28.5 × 1.15 = 32.78 board feet, so plan to buy about 33
Figure each line, add them, then round up once to what you will buy.
Softwood vs hardwood: which numbers go into the formula
The formula never changes, but how to calculate board feet correctly depends on the numbers you feed it, and those depend on the kind of lumber.
Board feet are figured on nominal dimensions. A USDA Forest Service glossary defines the board foot as a unit “based on the nominal dimensions” of the wood (USDA). So a 2x6 counts as 2 by 6 inches, although it is dressed to 1-1/2 by 5-1/2 inches dry (NIST PS 20-25, Table 3).
Plug in the actual size and a 2x6 gives 0.6875 board feet per foot instead of 1, about 31% short of the yard’s count.
Hardwood thickness is named in quarters of an inch of rough-sawn thickness, and the quarter is its nominal size. AHEC gives surfaced thickness as nominal minus 3/16 inch for stock 1-1/2 inches and thinner, and minus 1/4 inch for 1-3/4 inches and thicker.
| Quarter | Nominal (rough) thickness | Typical surfaced thickness | Board feet per foot, 6 in wide |
|---|---|---|---|
| 4/4 | 1 in | 13/16 in | 0.5 |
| 5/4 | 1-1/4 in | 1-1/16 in | 0.63 |
| 6/4 | 1-1/2 in | 1-5/16 in | 0.75 |
| 8/4 | 2 in | 1-3/4 in | 1 |
| 12/4 | 3 in | 2-3/4 in | 1.5 |
| 16/4 | 4 in | 3-3/4 in | 2 |
So a surfaced 4/4 board is about 13/16 inch thick but is still sold as 4/4, and board feet use that nominal 1 inch. Ask your dealer if their surfaced prices work differently. The last column uses the nominal thickness.
How a mill tallies a board (and why your total may differ)
Random-width hardwood is not measured to the sixteenth. In the export bundle tally AHEC describes, widths are rounded to the nearest whole inch and lengths down to the whole foot; the surface measure (width × length ÷ 12) is then rounded to a whole number and multiplied by the thickness.
That changes the count. A 4/4 board measuring 5-1/4 inches by 8-1/2 feet holds 3.72 board feet on a tape measure. Tallied, it is 5 inches by 8 feet: a surface measure of 3.33, rounded to 3, times 1 inch = 3 board feet.
You pay for the tally, so tally your boards the same way before you compare them with an invoice.
Price per board foot, per linear foot and per thousand board feet
Prices show up in three units, and the conversions all come from the same formula.
- Per board foot. Common for hardwood and specialty lumber. Multiply board feet by the price.
- Per linear foot. Common for trim and boards sold by length. A linear foot holds thickness × width ÷ 12 board feet, so price per linear foot = price per board foot × thickness × width ÷ 12.
- Per thousand board feet (MBF). The wholesale unit: the Random Lengths framing lumber composite is reported in dollars per thousand board feet (Fastmarkets). Divide by 1,000 for price per board foot.
At an example price of $4.80 per board foot (illustrative only), a linear foot of 4/4 x 8 costs $3.20 and a linear foot of 2x6 costs $4.80. An example wholesale price of $1,850 per MBF is $1.85 per board foot.
At that $4.80 example, the bookcase above, rounded up to 33 board feet, comes to $158.40 before tax and delivery.
Board feet in metric
One board foot is 0.00236 cubic meters, because 144 cubic inches at exactly 25.4 mm per inch (NIST Handbook 44) is 0.002359737216 m³. One cubic meter holds about 423.8 board feet.
The bookcase cut list, 32.78 board feet with the allowance, is about 0.077 cubic meters. Convert the final total, not each board, to avoid rounding drift. PS 20-25 figures board measure on nominal thickness and width (section 2.2), so board feet overstate the cubic meters of dressed lumber you actually receive.
Mistakes that throw off a board foot count
- Length in inches, divided by 12. The answer comes out twelve times too large; divide by 144 when all three measurements are in inches.
- Actual size for framing lumber. A 2x6 at actual size gives 0.6875 board feet per foot, about 31% under the yard’s nominal count.
- Planed thickness for hardwood. Surfaced 4/4 still counts as 1 inch, because board feet use the nominal quarter thickness.
- Rounding every board. On a long list the small roundings add up; round the final total once, upward.
- No allowance. Rough hardwood loses wood to defects and cuts; decide on an allowance before you order, not at the saw.
Avoid these five and you know how to calculate board feet the way a lumber yard does. For how every number on this site is produced and checked, see how we calculate.
