Board feet = thickness (inches) × width (inches) × length (feet) ÷ 12, so a 2x6 that is 12 feet long is exactly 12 board feet and a 2x4x8 is 5.33. This board foot calculator handles one size or a whole lumber list, adds a waste allowance, prices the order per board foot and shows the actual dressed volume next to the nominal (billed) volume.
Use it if you buy hardwood by the board foot, price framing packages, quote sawmill or slab lumber, or check a lumber yard invoice — it's a board feet calculator and a way to calculate lumber cost in one. You need the thickness and width in inches and the length in feet (or inches, which it converts).
How to calculate board feet
- Choose nominal for softwood sold as 2x4, 1x6 and similar, or actual for rough hardwood, live-edge slabs and anything you measured with a tape.
- Enter thickness and width in inches. For hardwood, 4/4 = 1, 5/4 = 1.25, 6/4 = 1.5 and 8/4 = 2.
- Enter the length in feet (or switch to inches) and the number of pieces. For mixed sizes, open the lumber list and type one line per size, such as
10, 2, 4, 8or6 @ 2x10x16. - Add a waste allowance and your price per board foot. The total, a per-line table and a CSV download appear on the right.
The board foot formula and where it comes from
A board foot is 1 inch × 12 inches × 1 foot, or 144 cubic inches. The American Softwood Lumber Standard, NIST Voluntary Product Standard PS 20-25 §2.2, defines board measure as nominal thickness in inches × nominal width in feet × length in feet. Writing the width in inches instead gives the familiar T × W × L ÷ 12. The American Hardwood Export Council's summary of the NHLA grading rules uses the same formula for hardwoods: width (in) × length (ft) × thickness (in) ÷ 12. When you know all three dimensions in inches, divide by 144 instead of 12.
The Forest Products Laboratory's Wood Handbook advises that board measure "depends on the thickness and width nomenclature used", so a buyer and seller should agree whether nominal or actual sizes are being tallied. That is why the calculator asks which you entered.
Nominal vs actual lumber sizes
A 2x4 is not 2 by 4 inches. PS 20-25 Table 3 sets the minimum dressed dry size (19% maximum moisture) for each nominal size, and softwood is billed on the nominal size. An 8 ft 2x4 is billed as 5.33 BF but contains 3.5 BF of dry wood, so the billed figure is 52% higher than the wood you actually get.
| Nominal | Actual dry size (in) | BF per linear ft | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft |
|---|---|---|---|---|---|---|---|
| 1×4 | 3/4 × 3-1/2 | 0.333 | 2.67 | 3.33 | 4 | 4.67 | 5.33 |
| 1×6 | 3/4 × 5-1/2 | 0.5 | 4 | 5 | 6 | 7 | 8 |
| 1×8 | 3/4 × 7-1/4 | 0.667 | 5.33 | 6.67 | 8 | 9.33 | 10.67 |
| 1×10 | 3/4 × 9-1/4 | 0.833 | 6.67 | 8.33 | 10 | 11.67 | 13.33 |
| 1×12 | 3/4 × 11-1/4 | 1 | 8 | 10 | 12 | 14 | 16 |
| 2×4 | 1-1/2 × 3-1/2 | 0.667 | 5.33 | 6.67 | 8 | 9.33 | 10.67 |
| 2×6 | 1-1/2 × 5-1/2 | 1 | 8 | 10 | 12 | 14 | 16 |
| 2×8 | 1-1/2 × 7-1/4 | 1.333 | 10.67 | 13.33 | 16 | 18.67 | 21.33 |
| 2×10 | 1-1/2 × 9-1/4 | 1.667 | 13.33 | 16.67 | 20 | 23.33 | 26.67 |
| 2×12 | 1-1/2 × 11-1/4 | 2 | 16 | 20 | 24 | 28 | 32 |
| 4×4 | 3-1/2 × 3-1/2 | 1.333 | 10.67 | 13.33 | 16 | 18.67 | 21.33 |
| 4×6 | 3-1/2 × 5-1/2 | 2 | 16 | 20 | 24 | 28 | 32 |
| 6×6 | 5-1/2 × 5-1/2 | 3 | 24 | 30 | 36 | 42 | 48 |
Sizes from nominal 5 inches up are timbers; PS 20-25 allows 1/2 in off for 5 and 6 in faces, 3/4 in for 7–15 in and 1 in for 16 in and larger, which is why a 6x6 dresses to 5-1/2 × 5-1/2 in.
Hardwood: quarters, rough and surfaced thickness
Hardwood is sold rough, in random widths, with thickness in quarters of an inch. You pay for the rough thickness even if you have the yard surface it. The USDA Wood Handbook (FPL-GTR-282, Table 6-4) lists the standard surfaced-two-sides (S2S) thickness for each rough size:
| Quarters | Rough thickness (in) | S2S thickness (in) | BF per sq ft of face | BF in an 8 in × 8 ft board |
|---|---|---|---|---|
| 4/4 | 1 | 13/16 | 1 | 5.33 |
| 5/4 | 1-1/4 | 1-1/16 | 1.25 | 6.67 |
| 6/4 | 1-1/2 | 1-5/16 | 1.5 | 8 |
| 7/4 | 1-3/4 | 1-1/2 | 1.75 | 9.33 |
| 8/4 | 2 | 1-3/4 | 2 | 10.67 |
| 10/4 | 2-1/2 | 2-1/4 | 2.5 | 13.33 |
| 12/4 | 3 | 2-3/4 | 3 | 16 |
| 14/4 | 3-1/2 | 3-1/4 | 3.5 | 18.67 |
| 16/4 | 4 | 3-3/4 | 4 | 21.33 |
Hardwood lengths come in 1-ft steps from 4 to 16 ft (Wood Handbook), and under the NHLA rules summarized by AHEC partial feet are dropped and widths are rounded to the nearest inch. So a 9 ft 7 in board is tallied as 9 ft. Measure the same way if you want your number to match the yard's.
Worked examples
- 2x4x8: 2 × 4 × 8 ÷ 12 = 5.333 BF.
- 2x10x16: 2 × 10 × 16 ÷ 12 = 26.67 BF.
- 4x4x10 post: 4 × 4 × 10 ÷ 12 = 13.33 BF.
- Mixed list: ten 2x4x8, six 2x10x16 and four 1x6x8 = 229.33 BF billed (157 BF actual wood); with 10% waste, order 252.27 BF.
- Rough oak: one 8/4 board, 7 in wide, 9 ft long = 2 × 7 × 9 ÷ 12 = 10.5 BF.
Price per board foot vs per piece
Some yards tag lumber per piece and others per board foot. To compare the two, divide the piece price by the piece's board feet. We don't show a default price because lumber prices move often and differ by region and species; enter the number from your yard's quote. Board feet per linear foot is thickness × width ÷ 12, so a 1x6 is 0.5 BF/ft and a 2x12 is 2 BF/ft — handy for converting a per-linear-foot price. For running lengths, the linear feet calculator totals trim and decking.
Board feet, MBF and cubic measure
Mills and wholesalers quote large orders per thousand board feet, abbreviated MBF or MBM (the Wood Handbook's list of lumber abbreviations defines both as "thousand (feet) board measure"). A price of P per MBF is P ÷ 1,000 per board foot, so divide by 1,000 before entering it here. Board feet convert to cubic feet by dividing by 12, because 12 board feet stacked make one cubic foot (12 × 144 = 1,728 cubic inches). The calculator shows the cubic feet of the billed size, which is useful for estimating shipping volume or drying-kiln capacity.
For a project, build the list from your cut list rather than from finished part sizes. Round each part up to a stock width and length you can actually buy, add the saw kerf and the length you lose squaring the ends, then enter the stock boards. For hardwood bought rough, also add the thickness you'll plane away: you pay for 4/4 even though the finished part is thinner.
Common mistakes
- Dividing by 144 with the length in feet. Use ÷ 12 when length is in feet and ÷ 144 when all three dimensions are in inches.
- Using actual size for softwood quotes. Yards bill nominal; using 1.5 × 3.5 for a 2x4 under-counts by 34% and your total won't match the invoice.
- Using S2S thickness for hardwood. 4/4 surfaced to 13/16 in is still sold as 1 in thick.
- Forgetting waste. Defects, end checks and cut-offs eat material. Set the waste percentage from your own cut list and the grade you buy; the 10% default is only a placeholder.
- Mixing up board feet and linear feet. A 16 ft 2x10 is 16 linear feet but 26.67 board feet.
Related calculators
Add up fractional cuts with the feet-inch-fraction construction calculator, total runs of trim with the linear feet calculator, size firewood in cords, or convert metric dimensions with mm to inches.
Frequently asked questions
What is the board foot formula?
Board feet = thickness (in) × width (in) × length (ft) ÷ 12. One board foot is a piece 1 in thick, 12 in wide and 1 ft long, 144 cubic inches. The American Softwood Lumber Standard (PS 20-25 §2.2) defines it with nominal sizes.
How many board feet are in a 2x4x8?
5.333 board feet: 2 × 4 × 8 ÷ 12. It is billed on the nominal 2 × 4 size even though the dry board measures 1-1/2 × 3-1/2 in, which is only 3.5 BF of actual wood.
How many board feet are in a 2x6x12?
Exactly 12 board feet (2 × 6 × 12 ÷ 12). A 2x6 has 1 BF per foot of length, which makes it easy to check a quote.
How many board feet in a 1x6x8?
4 board feet. A 1x6 holds 0.5 BF per linear foot, so 8 ft × 0.5 = 4.
Do you use nominal or actual size for board feet?
Softwood lumber yards bill on nominal size: PS 20 says board feet are found by multiplying nominal thickness by nominal width and length. Hardwood is tallied on rough thickness in quarters (4/4 = 1 in) and measured width. Switch the calculator to "actual" for hardwood or for the true volume of a dressed board.
What does 4/4, 5/4 and 8/4 mean?
Hardwood thickness in quarters of an inch: 4/4 is 1 in, 5/4 is 1-1/4 in and 8/4 is 2 in rough. Surfaced two sides they finish to about 13/16, 1-1/16 and 1-3/4 in (Wood Handbook Table 6-4), but board feet use the rough thickness.
How do I calculate the cost of lumber by the board foot?
Multiply total board feet (with waste) by the price per board foot. For a list of ten 2x4x8s, six 2x10x16s and four 1x6x8s that is 229.33 BF, or 252.27 BF with 10% waste. Enter your yard's price to see the total.
How many board feet in a 4x4x10?
13.33 board feet (4 × 4 × 10 ÷ 12).
How do I convert board feet to linear feet?
Divide board feet by the board feet per linear foot of the size (thickness × width ÷ 12). For 2x6 that is 1, so 120 BF is 120 linear feet; for 2x4 it is 0.6667, so 120 BF is 180 linear feet.
How do I measure a rough hardwood board?
Use rough thickness, measured width and length in feet. AHEC's summary of NHLA rules rounds odd widths to the nearest inch and drops partial feet of length. An 8/4 board 7 in wide and 9 ft long is 2 × 7 × 9 ÷ 12 = 10.5 BF.
Sources & method
- NIST, Voluntary Product Standard PS 20-25 American Softwood Lumber Standard — §2.2 board measure; Table 3 nominal and minimum dressed sizes
- USDA Forest Service, Forest Products Laboratory — Wood Handbook (FPL-GTR-282, 2021), Chapter 6: Commercial Lumber, Round Timbers, and Ties (Table 6-4)
- American Hardwood Export Council — Grading sawn lumber: Measurement (NHLA rules, quarter thicknesses, board foot tally)
- NIST, PS 20-20 Revision 1 (October 2021) — previous edition with the same board measure definition
Results are estimates for general information. Found an error? It helps everyone — see our methodology.