Board Feet and MBF Explained
Board feet are not a measure of wood. They are a measure of the log the wood came out of, and the two stopped agreeing the day lumber started being planed. The formula takes ten seconds. Understanding what the answer contains is the part that decides whether you order enough, and whether a price per board foot means anything when you compare two sizes.
The formula, and the one word that does all the work
A board foot is nominal thickness in inches, times nominal width in inches, times length in feet, divided by twelve. A 2x4 eight feet long is 2 x 4 x 8 / 12, which is 5.33 board feet.
Nominal is the word that matters. It means the size the board was named at the saw, not the size it measures now. The American Softwood Lumber Standard, PS 20, sets the finished dimensions lumber is dressed to, and those are the numbers on a tape measure: a 2x4 is 1 1/2 by 3 1/2 in, a 2x6 is 1 1/2 by 5 1/2, a 2x12 is 1 1/2 by 11 1/4. The board foot ignores all of that and bills you on the two and the four.
One board foot is defined as one twelfth of a cubic foot. So if lumber were sold at its sawn size the two units would be interchangeable and nobody would need this page. Lumber is not sold at its sawn size, which is why every board foot figure on an invoice is larger than the wood in the pile.
The division by twelve is the only conversion in the formula, and it exists because thickness and width are in inches while length is in feet. Put all three in inches and divide by 144 instead. The answer is the same and the mistake is less likely.
What a board foot actually contains
Take the dressed area of a section, divide it by the nominal area, and you have the fraction of each billed board foot that is physically there. A 2x4 is 5.25 square inches of wood billed as 8, which is 66% of what the unit promises. Run that across the common sizes and the spread is wider than most people expect.
| Nominal size | Board feet per ft of length | Cu ft of wood per MBF | Nominal volume not present |
|---|---|---|---|
| 1x4 | 0.333 | 54.7 | 34% |
| 1x6 | 0.500 | 57.3 | 31% |
| 1x8 | 0.667 | 56.6 | 32% |
| 2x4 | 0.667 | 54.7 | 34% |
| 2x6 | 1.000 | 57.3 | 31% |
| 2x8 | 1.333 | 56.6 | 32% |
| 2x10 | 1.667 | 57.8 | 31% |
| 2x12 | 2.000 | 58.6 | 30% |
| 4x4 | 1.333 | 63.8 | 23% |
| 6x6 | 3.000 | 70.0 | 16% |
Here is the finding, and it is the reason this page exists: a thousand board feet is not a fixed quantity of wood. Since one board foot is one twelfth of a cubic foot by definition, an MBF would always be 83.3 cu ft if lumber arrived at its nominal size. It does not, so an MBF of 2x4 is 54.7 cu ft of actual timber and an MBF of 6x6 is 70.0. The 6x6 delivers 28% more wood for the same billed quantity.
That is arithmetic on two published things, the definition of the unit and the PS 20 dressed sizes, and it is not a complaint about the trade. It is a caution about comparison. A price per board foot is only comparable between two boards of the same section, and a mill quote that covers a mixed order is quoting a unit whose wood content changes item by item.
The pattern behind the numbers is simple once you see it. Dressing removes a fixed amount from each dimension: a quarter of an inch off a 1 in nominal, half an inch from 2 in through 6 in, and three quarters of an inch at 8 in and above. A fixed loss is a bigger proportion of a small section. That is why the worst case in the table is the smallest and squarest common size, and why posts do best.
MBF, and how to turn a mill quote into pieces
MBF is a thousand board feet. The M is the Roman numeral for a thousand, not the metric prefix, and it is the unit mills, futures and market reports quote in. A quote of 600 dollars per MBF is 60 cents a board foot. A quote of 60 cents a board foot is 600 dollars per MBF. There is nothing else to the conversion.
What is genuinely awkward is going from MBF to a pile on a truck, because that depends entirely on the section. The table below is the same arithmetic run the other way.
| Nominal size | Linear feet in 1 MBF | 8 ft pieces | 16 ft pieces |
|---|---|---|---|
| 1x6 | 2,000 lf | 250 pieces | 125 pieces |
| 2x4 | 1,500 lf | 188 pieces | 94 pieces |
| 2x6 | 1,000 lf | 125 pieces | 63 pieces |
| 2x8 | 750 lf | 94 pieces | 47 pieces |
| 2x10 | 600 lf | 75 pieces | 38 pieces |
| 2x12 | 500 lf | 63 pieces | 32 pieces |
| 4x4 | 750 lf | 94 pieces | 47 pieces |
| 6x6 | 333 lf | 42 pieces | 21 pieces |
Read the 2x4 row and the 6x6 row together and the earlier point becomes physical. A thousand board feet is 188 eight-foot studs or 42 eight-foot posts, and the posts are the heavier load by a comfortable margin even though the invoice says the same thing.
Retail works the other way round. Dimensional lumber on a rack is priced by the piece, so converting a shelf price back to a board foot price is the only way to compare two sizes honestly. Divide the piece price by the board feet in that piece: a 2x4x8 is 5.33 bf, a 2x6x8 is 8.00 bf, a 2x8x8 is 10.67 bf. If the 2x6 is not at least 1.5 times the price of the 2x4, it is the cheaper wood by the board foot, before you account for the fact that it also loses slightly less to dressing.
Where the unit belongs, and where it does not
Board feet earn their keep on hardwood, which is sold in random widths and lengths. There is no piece price to quote because there is no standard piece, so volume is the only sensible unit. Hardwood thickness is quoted in quarters of an inch: 4/4 is one inch nominal, 5/4 is an inch and a quarter, 8/4 is two inches. A 4/4 board six inches wide and eight feet long is 1 x 6 x 8 / 12, which is 4 board feet, and the same quarter convention is why a 5/4x6 deck board is named the way it is.
They are the wrong unit for sheet goods. Plywood and OSB are sold by the sheet and specified by span rating, not by volume, and converting a sheet to board feet tells you nothing you can buy with.
They are an awkward unit for framing, because a wall is built out of specific lengths rather than a volume. Order framing in pieces and check the invoice in board feet. That is the split the framing calculators on this site use: pieces to buy from, board feet to audit with.
Rough sawn stock is the one case where the two numbers nearly agree. It has not been dressed, so a rough 2x4 is close to a genuine two by four and its board feet are close to real volume. Anyone pricing rough stock against dressed stock per board foot is comparing a unit that is roughly honest against one that is a third short.
Weight, and the term with the widest spread
Board feet are often the route to a weight, for a delivery, a lift or a floor load, and this is where the arithmetic stops being reliable. Weight is water weight, and it moves more than anything else in the calculation.
Work the volume first, because the weight belongs to the wood and not to the billing unit. A hundred 2x4s eight feet long is 533 board feet on the invoice and 29.2 cu ft of actual timber. At 30 lb per cubic foot, typical for kiln dried softwood, that is 875 lb, about 8.8 lb a stick. The same hundred boards green off the saw are nearer 1,370 lb, and freshly treated stock heavier again because the preservative is carried in water.
Multiplying board feet by a density figure skips the dressing loss and overstates the load by roughly a third on small sections. The USDA Wood Handbook is the reference behind any density figure worth using, and it is also the reason the figures come as ranges: specific gravity varies by species and the moisture content varies by the week. If the weight matters, weigh a piece.
What the numbers do not tell you: price
This site publishes no lumber price of its own, because no free, citable, current retail price per board foot exists to publish. What does exist is the US Bureau of Labor Statistics Producer Price Index for softwood lumber, series WPU0811, which is free, dated and revised on a schedule. It stood at 300.614 in July 2026, up 15.0% on July 2025.
An index cannot tell you what a board costs. It tells you which direction a quote you were given six months ago has aged in, which is a different and more honest question. On the figures above, a price quoted before July 2025 is likely to be low.
Last price check: September 7, 2026.
What this guide does not decide
It does not size anything. Board feet are a billing and ordering unit, and nothing in them speaks to whether a member spans, carries or complies. A 2x4 wall under two floors plus a roof is outside IRC Table R602.3(5) regardless of how neatly the board feet work out.
It does not price lumber, and it does not convert species. A board foot of cedar and a board foot of southern pine are the same volume at very different money and very different weight.
And it assumes dressed softwood to PS 20. Rough sawn, resawn, imported stock and anything graded outside that standard can measure something else, in which case measure it.
Run the numbers
- Board Foot Calculator board feet, MBF, actual volume and weight side by side
- Wall Framing Calculator studs and plates in pieces, audited in board feet
- Deck Lumber Calculator boards and joists on actual widths, not nominal
- Sheathing Calculator where sheets replace board feet entirely
- Beam Calculator when the question is whether it spans, not what it costs
- Deck Materials Calculator a whole deck takeoff in build order
Frequently asked questions
- How do you calculate board feet?
- Multiply nominal thickness in inches by nominal width in inches by length in feet, then divide by twelve. A 2x4 that is eight feet long is 2 x 4 x 8 / 12, which is 5.33 board feet. If you prefer to work entirely in inches, multiply all three dimensions in inches and divide by 144 instead.
- What is MBF?
- A thousand board feet. The M is the Roman numeral for a thousand, so MBF is the unit mills and market reports quote in, and 600 dollars per MBF is the same as 60 cents per board foot. It is not a metric prefix and it does not mean a million.
- Is a board foot the same as a cubic foot?
- A board foot is defined as one twelfth of a cubic foot, so twelve board feet would be a cubic foot if the wood were really there. It is not, because lumber is billed at its nominal size and delivered at its dressed size. On a 2x4 only about 66% of the billed volume is physically present.
- How many board feet are in a 2x4, a 2x6 and a 2x8?
- Per foot of length, a 2x4 is 0.667 board feet, a 2x6 is 1.0 and a 2x8 is 1.333. So an eight foot 2x4 is 5.33 bf, an eight foot 2x6 is 8 bf and an eight foot 2x8 is 10.67 bf. Multiply the per-foot figure by whatever length you are buying.
- How many 2x4s are in a thousand board feet?
- One hundred and eighty eight eight-foot 2x4s, or ninety four sixteen-foot ones, because a 2x4 carries 0.667 board feet per foot of length. The same MBF in 6x6 is only about forty two eight-foot posts, and that pile contains 28% more actual wood.
- Why is a 2x4 not two inches by four inches?
- It is sawn at two by four and then dried and dressed on all four sides, which takes material off. PS 20, the American Softwood Lumber Standard, sets the finished sizes at 1 1/2 by 3 1/2 in, and the trade convention is that the board keeps the name and the billing of the size it was sawn at.
- How do I convert a price per board foot to a price per piece?
- Multiply the board feet in that piece by the price per board foot. A 2x4x8 at 60 cents per board foot is 5.33 x 0.60, which is 3.20 dollars. Going the other way, divide a shelf price by the board feet in the piece, which is the only way to compare a 2x4 against a 2x6 fairly.
- How do you calculate board feet for hardwood sold in quarters?
- Quarters are nominal thickness in quarter inches, so 4/4 is one inch, 5/4 is an inch and a quarter and 8/4 is two inches. Use that as the thickness in the ordinary formula: a 4/4 board six inches wide and eight feet long is 1 x 6 x 8 / 12, which is 4 board feet.
Check these numbers yourself
- PS 20, American Softwood Lumber StandardAmerican Lumber Standard Committee. The dressed size tables that set a 2x4 at 1 1/2 by 3 1/2 in and every other figure in the tables above. Free PDF. Dressed sizes read for this site on 2026-09-08.
- American Lumber Standard CommitteeThe committee that administers PS 20 and accredits the grading agencies whose stamps appear on lumber.
- USDA Wood Handbook, Wood as an Engineering MaterialForest Products Laboratory. Specific gravity and moisture relations, which is where wood density figures come from and why they are published as ranges.
- US Bureau of Labor Statistics, Producer Price Index, softwood lumber, series WPU0811US Bureau of Labor Statistics. 300.614 in July 2026, 15.0% above July 2025. Read 2026-09-07.
- IRC Table R602.3(5), size, height and spacing of wood studsUpCodes, 2021 IRC as adopted in the 2022 Connecticut State Building Code. Used because codes.iccsafe.org returns HTTP 403. Cited here only for the point that board feet decide nothing structural.
Figures here last checked against the source documents on 2026-09-16. Codes are amended locally; confirm against the edition your jurisdiction enforces.
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