Board Foot Calculator
Board feet for hardwood priced by volume, where nominal and actual sizes differ.
Updated
You need
32.00board feet
8 pieces across 2 rows
- 6 × 1 in × 6 in × 8 ft
- 24.00 bf
- 2 × 2 in × 4 in × 6 ft
- 8.00 bf
Board feet are figured on NOMINAL rough dimensions, which is how hardwood is sold. Surfaced stock measures less than it is billed at.
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In short
How do I calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 4/4 board 6 in wide and 8 ft long is 1 times 6 times 8 divided by 12, which is 4 board feet. If the length is in inches instead, divide by 144, because one board foot is 144 cubic inches.
Board feet are always figured on the nominal rough dimensions, which is how hardwood is graded and sold. Surfaced stock measures less than you are billed for, and that is normal rather than a mistake.
How to use the board foot calculator
A board foot is a volume, not a length or an area, and that single fact explains most of the confusion around it. One board foot is 144 cubic inches: a piece one inch thick, twelve inches wide and twelve inches long. Any other shape holding the same volume is also one board foot.
So start by choosing the quarter thickness. Rough hardwood is sold in quarters of an inch, which is why the sizes read as fractions: 4/4 is one inch, 5/4 is an inch and a quarter, 8/4 is two inches. The number on top counts quarter inches, and the four underneath never changes.
4.00
Board feet in a 4/4 by 6 by 8 ft
1 × 6 × 8 ÷ 12
144
Cubic inches in one board foot
1 in × 12 in × 12 in
13/16 in
A surfaced 4/4 board
still sold as a full inch
Then enter the width in inches and the length in feet. Those are the units a lumber yard lists stock in, and they are why the divisor is 12 rather than 144. If you would rather work entirely in inches, use the length in inches and divide by 144 instead; the answer is identical.
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Use the extra rows for anything in your cut list that differs in size. Board feet do not scale in a way you can eyeball, because three dimensions are moving at once. A 4/4 board 6 inches by 8 feet is 4 board feet, while an 8/4 board 8 inches by 10 feet is 13.33, and neither number is obvious from looking at the pile.
The total is the number that travels. Hardwood is priced per board foot, so a volume total lets you compare a quote in cherry against a quote in walnut, or one yard against another, without translating between piece counts and lengths. A piece count tells you nothing until you know how big the pieces are.
Buying softwood by the piece instead
Decking, joists and framing are sold as counted pieces at fixed lengths, which is a different sum entirely from pricing hardwood by volume.
Open the deck calculator →One habit worth building: buy more board feet than your cut list says. Rough lumber arrives with wane, checks, bow and the odd defect, and flattening and squaring a rough board consumes thickness and width before you get to the part you keep. Exactly how much extra depends on the grade and on how forgiving your design is.
Do
- Use the nominal quarter thickness, so 1 inch for 4/4 rather than 13/16.
- Enter width in inches and length in feet, then let the divisor be 12.
- Total a mixed cut list row by row rather than averaging the sizes.
- Buy extra board feet to cover defects and the loss in flattening rough stock.
- Compare species and suppliers on price per board foot, not per piece.
Don't
- Measure a surfaced board with a caliper and bill yourself for that thickness.
- Expect a 2x4 to contain the board feet its nominal name suggests.
- Confuse a board foot with a linear foot, which measures length alone.
- Assume hardwood arrives in the fixed lengths softwood comes in.
- Price a rough board as if every inch of it will end up in the project.
Board feet for common hardwood sizes across the quarter thicknesses, at three face sizes. Read down a column to see what thickness costs you, and across a row to see how quickly width and length stack up in a cut list.
| Thickness | Nominal inches | 6 in × 8 ft | 8 in × 8 ft | 10 in × 10 ft |
|---|---|---|---|---|
| 4/4 | 1 | 4.00 bf | 5.33 bf | 8.33 bf |
| 5/4 | 1 1/4 | 5.00 bf | 6.67 bf | 10.42 bf |
| 6/4 | 1 1/2 | 6.00 bf | 8.00 bf | 12.50 bf |
| 8/4 | 2 | 8.00 bf | 10.67 bf | 16.67 bf |
| 12/4 | 3 | 12.00 bf | 16.00 bf | 25.00 bf |
| 16/4 | 4 | 16.00 bf | 21.33 bf | 33.33 bf |
Reading 4/4, 5/4 and 8/4 without guessing
Quarter thickness survives because rough hardwood is milled and graded in quarter inch steps. The notation is simply that fraction written out: the top number counts quarter inches and the bottom is always four. Four quarters is one inch, five quarters is an inch and a quarter, eight quarters is two inches.
The reason it feels strange is that softwood does not work this way. Dimensional softwood is named in whole inches that it does not actually measure, whereas hardwood quarters are honest about the rough size and simply do not promise you what arrives after surfacing.
What that costs you in practice is worth seeing in numbers. A 4/4 board 6 inches wide and 8 feet long is 4 board feet on the nominal inch. Figure the same board on its 13/16 inch surfaced thickness and it comes to 3.25 board feet. That 0.75 of a board foot per board is not an error in the bill, it is planer shavings.
- 4/4 (1 in)
- 4.00 board feet
- 5/4 (1 1/4 in)
- 5.00 board feet
- 6/4 (1 1/2 in)
- 6.00 board feet
- 8/4 (2 in)
- 8.00 board feet
- 12/4 (3 in)
- 12.00 board feet
- 16/4 (4 in)
- 16.00 board feet
Thickness scales the volume directly, so 8/4 stock is exactly twice the board feet of 4/4 at the same face size. It is usually more than twice the price, because thicker boards are harder to dry without degrade.
Why a 2x4 is not two inches by four
Softwood dimensional lumber is named nominally and sold by the piece, which is a completely different commercial system from hardwood. A 2x4 measures 1 1/2 by 3 1/2 inches dressed and dry, and that is not a defect or a shortcut: it is fixed by Voluntary Product Standard PS 20, the American Softwood Lumber Standard.
The nominal name refers roughly to the green, rough sawn size before the board was dried and planed. PS 20 pinned the finished dimensions so that a 2x4 from any mill in the country would frame against a 2x4 from any other, and the actual figures have not moved since the standard first landed in 1964.
Run the board foot arithmetic on both and the gap is stark. An 8 foot 2x4 figured on its nominal 2 by 4 inches is 5.33 board feet, while the same stick figured on its real 1 1/2 by 3 1/2 inches is 3.5 board feet, about 66 percent of the nominal volume. That is exactly why softwood is not sold this way.
The practical rule is simple. If you are buying hardwood, think in board feet and use the nominal quarter thickness. If you are buying framing, decking or dimensional softwood, count pieces at fixed lengths and let the board foot arithmetic go, because the price on the shelf is already a price per stick.
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The formula, worked line by line
The definition comes first and everything else follows from it. One board foot is 144 cubic inches of wood: a piece one inch thick, twelve inches wide and twelve inches long. It is a unit of volume, so any shape enclosing 144 cubic inches is one board foot.
From there the arithmetic is just unit bookkeeping. Multiply the three dimensions in inches and divide by 144, and you have the number of 144 cubic inch parcels in the board. That is the general form, and it works whatever units you started in as long as you convert.
The version you will actually use has the length in feet, because that is how lumber is listed. Twelve of the 144 cancels against the twelve inches in a foot, leaving a divisor of 12. The two forms are the same equation, and they give the same answer.
board feet = (thickness in × width in × length in) ÷ 144
board feet = (thickness in × width in × length FT) ÷ 12
row total = board feet per piece × quantity
cut list total = sum of every row- Six 4/4 boards, 6 in × 8 ft
- 1 × 6 × 8 ÷ 12 = 4.00 bf each
- That row
- 6 × 4.00 = 24.00 bf
- Two 8/4 boards, 4 in × 6 ft
- 2 × 4 × 6 ÷ 12 = 4.00 bf each
- That row
- 2 × 4.00 = 8.00 bf
- Cut list total
- 32.00 board feet
Notice that a 4/4 board 6 inches by 8 feet and an 8/4 board 4 inches by 6 feet are both exactly 4 board feet, despite looking nothing alike. Twice the thickness against two thirds the width and three quarters the length happens to cancel out perfectly, which is the clearest possible demonstration that this is a volume.
Checking the definition against itself is a good habit. A board one inch thick, twelve inches wide and one foot long gives 1 times 12 times 1 divided by 12, which is exactly 1. If your arithmetic does not return 1 for that board, you have the divisor wrong.
The thing the formula will not do is warn you about nominal dimensions, so that is on you. Every figure here assumes the size the board was graded and sold at. A surfaced 4/4 board really does measure about 13/16 of an inch, and putting that measured figure into the formula will underbill you by roughly a fifth on every board.
Prices are the one thing this page will not print. What a board foot costs depends on species, grade, thickness, width, whether it is surfaced, and where you are standing, and every one of those moves it. Take the volume total to a supplier and get a current quote against it, which is exactly what the number is for.
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Questions people ask
What is a board foot?
A board foot is 144 cubic inches of lumber, which is the volume of a piece one inch thick, twelve inches wide and twelve inches long. Because it is a volume rather than a length or an area, any board holding the same amount of wood counts as one board foot regardless of its shape. That is what makes it useful for trading hardwood, where boards arrive in random widths and lengths and a piece count would tell a buyer nothing at all about how much wood is being sold.
What does 4/4 mean in lumber?
It means four quarters of an inch, so one inch of nominal thickness, and it is how rough hardwood is milled, graded and sold. The notation continues in quarter inch steps: 5/4 is an inch and a quarter, 6/4 is an inch and a half, 8/4 is two inches, and 16/4 is four. The critical word is nominal. A 4/4 board is one inch as sawn, but surfacing removes roughly 3/32 of an inch from each face, and the standard surfaced thickness under the National Hardwood Lumber Association rules is 13/16 of an inch. You are billed on the inch.
How many board feet are in a 2x4?
That depends on whether you use the name or the actual size, and the gap is the whole point. An 8 foot 2x4 figured on its nominal 2 by 4 inches comes to 5.33 board feet, while the same stick figured on its real 1 1/2 by 3 1/2 inches comes to 3.5 board feet, about 66 percent as much. Those actual dimensions are fixed by Voluntary Product Standard PS 20, the American Softwood Lumber Standard. In practice nobody buys a 2x4 by the board foot at all, because dimensional softwood is sold as counted pieces at fixed lengths.
Why is hardwood sold by the board foot but softwood by the piece?
Because they arrive in completely different shapes. Softwood dimensional lumber is milled to a small set of standard sizes and lengths, so a 2x4x8 is an interchangeable unit and a price per piece works perfectly. Hardwood is cut to get the most usable wood out of each log, so boards come in random widths and random lengths, and no two are the same. A price per piece would be meaningless, whereas a price per board foot prices the actual wood. It is the same reason you buy eggs by the dozen and flour by weight.
How many extra board feet should I buy?
More than your cut list says, though the exact margin depends on the grade you are buying and how forgiving your design is. Rough lumber comes with wane along the edges, checks at the ends, bow and twist along its length, and the occasional knot or defect you have to cut around. Flattening and squaring a rough board also consumes real thickness and width before you reach the part you keep. A lower grade needs a bigger allowance because more of the board is unusable, and a project with long, wide, defect free parts needs more than one made of small pieces.
Sources
Where the constants and formulas on this page come from. Each line names the figure it backs.
The dressed dry dimensions of nominal softwood that make a 2x4 measure 1 1/2 by 3 1/2 inches — fixed by standard, not by the mill.
Voluntary Product Standard PS 20-20, American Softwood Lumber Standard — NIST, PS 20-20
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