🪵 Board Foot Calculator: Lumber Board Feet and Cost
By Shihab Mia · Updated 2026-06-26
A board foot is 144 cubic inches of lumber (12 in x 12 in x 1 in). Board feet = thickness x width x length in inches, divided by 144. Add a 10 to 15 percent waste allowance when buying.
A board foot is the unit hardwood lumber is sold in, and it is easy to mix up with a linear foot or a square foot. This calculator does the conversion for you: enter the thickness and width in inches, the length in feet or inches, and how many boards you are buying. You get the total board feet, plus the cost if you add a price per board foot. It is the fastest way to check a lumber quote or work out how much to order for a project.
What is the Board Foot Calculator?
A board foot (often shortened to BF or bd ft) is a measure of lumber volume, not length or area. One board foot equals 144 cubic inches: a piece of wood 12 inches long, 12 inches wide and 1 inch thick. The same volume can take many shapes, so a board 1 inch by 12 inches by 1 foot, a board 2 inches by 6 inches by 1 foot, and a board 1 inch by 6 inches by 2 feet are all exactly one board foot. Hardwood lumber yards quote prices per board foot precisely because it captures volume regardless of the cut, which matters when boards come in random widths and lengths sorted by grade rather than by a fixed size.
The formula is simply the volume in cubic inches divided by 144. With every dimension in inches, board feet = (thickness x width x length) / 144. Because lumber length is usually given in feet, there is a handy shortcut: board feet = (thickness x width x length in feet) / 12, since 144 cubic inches divided by 12 inches per foot leaves 12. Both versions give the same answer, and the calculator above uses whichever unit you pick for the length field. When you buy a stack of identical boards, multiply the board feet of one board by the quantity, then multiply by the price per board foot to get your total cost.
One point that trips people up is nominal versus actual size. A board sold as a '1x6' or a '2x4' is named for its rough-sawn size before drying and planing, but the finished board is smaller, a 2x4 is actually about 1.5 by 3.5 inches. For pricing, hardwood is always measured by its rough nominal dimensions, and thickness under one inch is still counted as a full inch. You are paying for the original rough lumber volume because the mill did the work of drying and surfacing it down to the finished size. When in doubt, ask the supplier which dimensions their board-foot price is based on so your estimate matches their invoice.
Hardwood thickness is often written in quarter-inch units, a system called quarter notation. A 4/4 board (said 'four quarter') is one inch nominal, 5/4 is one and a quarter inches, 6/4 is one and a half, and 8/4 is two inches. This notation always refers to the rough-sawn thickness, so a 4/4 board planed to three-quarters of an inch is still billed as a full inch in the board-foot math. Knowing the quarter system makes it far easier to read a hardwood price list and to enter the right thickness here: pick the nominal inch value (1 for 4/4, 2 for 8/4, and so on).
Width and length behave differently from thickness. Hardwood is often sold in random widths and random lengths, so a single bundle can hold boards from four inches to twelve inches wide. To estimate a bundle, you can total the board feet board by board, or use an average width if the mix is consistent. For softwood framing lumber sold in fixed dimensions, the nominal size on the tag (2x4, 2x6, 2x10) is what you plug in, even though the planed board is smaller. Either way, the calculator returns true volume, which is the only fair basis for comparing prices between boards of different sizes.
Finally, remember that the calculated board feet is the wood you need in the finished project, not the wood you should buy. Real boards have knots, splits, checks and bowed ends, and cutting parts to length always leaves offcuts. Most woodworkers add a waste allowance of 10 to 15 percent on top of the calculated figure, and more for short parts, curved cuts or figured stock where defects must be cut around. Building that cushion into your order is the difference between finishing a project in one trip and making a second run to the lumber yard.
When to use it
- Checking a hardwood lumber quote so you know whether the price per board foot is fair.
- Working out how many board feet a furniture or woodworking project needs before you shop.
- Comparing two boards of different sizes on a true volume (and therefore cost) basis.
- Estimating the total material cost of a stack of lumber from a single price per board foot.
- Translating a hardwood price list written in quarter notation (4/4, 6/4, 8/4) into real dollars per board.
- Adding a waste allowance so a random-width, random-length bundle covers the parts your plan calls for.
How to use the Board Foot Calculator
- Enter the board thickness in inches (for example 1 for a 1x or 4/4 board, 2 for a 2x or 8/4 board).
- Enter the board width in inches (use the nominal width on the tag, or the measured width for random-width hardwood).
- Enter the length and choose feet or inches from the unit dropdown.
- Set the quantity (number of identical boards) you are buying.
- Optionally add a price per board foot to see the total and per-board cost.
- Add roughly 10 to 15 percent to the result as a waste allowance before you place the order.
Formula & method
Worked examples
You are buying ten boards, each 1 inch thick, 6 inches wide and 8 feet long, at $4.50 per board foot.
- Convert length to inches: 8 ft x 12 = 96 in
- Board feet per board = (1 x 6 x 96) / 144 = 576 / 144 = 4 BF
- Total board feet = 4 x 10 = 40 BF
- Cost = 40 x $4.50 = $180.00
Result: 40 board feet total, $180.00 (4 BF and $18.00 per board)
You need five 2 in x 10 in x 12 ft boards priced at $3.20 per board foot.
- Using the feet shortcut: board feet = (thickness x width x length in feet) / 12
- Board feet per board = (2 x 10 x 12) / 12 = 240 / 12 = 20 BF
- Total board feet = 20 x 5 = 100 BF
- Cost = 100 x $3.20 = $320.00
Result: 100 board feet total, $320.00 (20 BF and $64.00 per board)
A table project calls for 18 board feet of 8/4 walnut at $12 per board foot, and you want a 15 percent waste cushion.
- Note that 8/4 means 2 inches nominal thickness, the figure you would enter for thickness
- Add waste: 18 BF x 1.15 = 20.7 BF, round up to 21 BF to order
- Cost of the wood you need = 18 x $12 = $216.00
- Cost of the order with waste = 21 x $12 = $252.00
Result: Order about 21 board feet, roughly $252.00 including a 15 percent waste allowance
Board feet for one board by nominal size and length
| Nominal size | 8 ft | 10 ft | 12 ft |
|---|---|---|---|
| 1 in x 4 in | 2.67 BF | 3.33 BF | 4.00 BF |
| 1 in x 6 in | 4.00 BF | 5.00 BF | 6.00 BF |
| 1 in x 8 in | 5.33 BF | 6.67 BF | 8.00 BF |
| 2 in x 4 in | 5.33 BF | 6.67 BF | 8.00 BF |
| 2 in x 6 in | 8.00 BF | 10.00 BF | 12.00 BF |
| 2 in x 10 in | 13.33 BF | 16.67 BF | 20.00 BF |
Quarter notation to nominal thickness
| Quarter | Nominal thickness | Typical surfaced thickness |
|---|---|---|
| 4/4 | 1 in | 13/16 in |
| 5/4 | 1.25 in | 1-1/16 in |
| 6/4 | 1.5 in | 1-5/16 in |
| 8/4 | 2 in | 1-3/4 in |
| 12/4 | 3 in | 2-3/4 in |
| 16/4 | 4 in | 3-3/4 in |
Common lumber units compared
| Unit | What it measures | Used for |
|---|---|---|
| Board foot | Volume (144 cubic inches) | Hardwood lumber pricing |
| Linear foot | Length only | Trim, moulding, dimensional lumber |
| Square foot | Surface area | Flooring, sheet goods, decking coverage |
Common mistakes to avoid
- Confusing board feet with linear feet. A linear foot only measures length, while a board foot measures volume. Two boards of the same length can hold very different amounts of wood, so always price hardwood by the board foot, not the running foot.
- Dividing by 12 when the length is in inches. The divide-by-12 shortcut only works when the length is in feet. If every dimension is in inches you must divide by 144. Mixing the two inflates or shrinks the result by a factor of twelve.
- Using the finished (actual) size instead of nominal. A 2x4 is really about 1.5 by 3.5 inches once planed, and a 4/4 board is often surfaced to 3/4 inch, but hardwood is always priced on its rough nominal size. Enter the nominal dimensions so the estimate matches the invoice.
- Forgetting a waste allowance. Offcuts, knots, splits and trimming to length all eat into usable wood. Order roughly 10 to 15 percent more board feet than the project drawing calls for so you are not caught short.
- Misreading quarter notation. Quarter notation counts quarter-inches, so 5/4 is 1.25 inches and 8/4 is 2 inches, not five or eight inches. Enter the nominal inch value for thickness, not the raw number in the fraction.
- Averaging random-width boards carelessly. Hardwood often comes in random widths, so a single average width can over or under count a mixed bundle. For an accurate total, tally each board, or measure a representative average if the spread is small.
Glossary
- Board foot (BF)
- A unit of lumber volume equal to 144 cubic inches, the same as a piece 12 in long, 12 in wide and 1 in thick.
- Nominal size
- The rough-sawn size a board is named for (such as 2x4 or 4/4) before it is dried and planed to a smaller finished size.
- Actual (surfaced) size
- The real measured size of a board after drying and planing, smaller than nominal but not used for board-foot pricing.
- Linear foot
- A measure of length only, one foot along a board regardless of its width or thickness.
- Quarter notation
- Hardwood thickness expressed in quarter-inches: 4/4 is one inch, 6/4 is one and a half, 8/4 is two inches rough.
- Random width and length (RWL)
- Hardwood sold in mixed widths and lengths sorted by grade, priced by total board feet rather than a fixed size.
- Waste allowance
- Extra material added to an order to cover offcuts, defects and trimming, usually 10 to 15 percent.
- Grade
- A quality rating (such as FAS or No. 1 Common) that describes how much clear, defect-free wood a board yields.
Frequently asked questions
How do you calculate board feet?
Multiply the thickness, width and length in inches, then divide by 144. For example a board 1 inch thick, 6 inches wide and 96 inches (8 feet) long is (1 x 6 x 96) / 144 = 4 board feet. If the length is in feet, divide by 12 instead of 144.
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches. It is the volume of a board 12 inches long, 12 inches wide and 1 inch thick. Hardwood is sold by the board foot because it measures the actual amount of wood regardless of how the board is cut.
Is a board foot the same as a linear foot?
No. A linear foot measures length only, while a board foot measures volume (thickness x width x length). Two boards of equal length can contain very different amounts of wood, so they are priced differently per board foot.
Should I use the nominal or actual size?
Always use the nominal (rough-sawn) size. Hardwood is measured and priced by its rough nominal dimensions, and thickness under one inch is counted as a full inch. A 4/4 board surfaced to 3/4 inch is still billed at a full inch. Ask your supplier which dimensions their board-foot price is based on if you are unsure.
What does 4/4, 6/4 or 8/4 mean in board feet?
Those are quarter-notation thicknesses. 4/4 is one inch nominal, 5/4 is 1.25 inches, 6/4 is 1.5 inches and 8/4 is two inches. Enter the nominal inch value as the thickness. For example, 8/4 oak 6 inches wide and 8 feet long is (2 x 6 x 96) / 144 = 8 board feet.
How much extra lumber should I order?
Add roughly 10 to 15 percent to your calculated board feet to cover offcuts, knots, splits and trimming to length. For intricate pieces, short parts or figured stock with lots of waste, allow 20 percent or more.
How do I find the total cost of my lumber?
Multiply the total board feet by the price per board foot. This calculator does it automatically when you enter a price, and also shows the cost per individual board so you can compare options. Typical hardwoods like oak and maple run about $4 to $10 per board foot, with walnut and figured species costing more.
How do I calculate board feet for random-width boards?
Tally each board separately using its own measured width, then add the board-foot totals together. If the widths are fairly consistent you can use an average width, but tallying board by board is more accurate for a mixed bundle of hardwood.
Why is hardwood sold by the board foot instead of by the piece?
Hardwood comes in random widths and lengths sorted by grade, so a 12-inch-wide board holds far more usable wood than a 6-inch board of the same length. Pricing by board foot charges for actual volume, which is fair to both the buyer and the mill.
How many board feet are in a 2x4x8?
A 2x4 that is 8 feet long is (2 x 4 x 8) / 12 = 5.33 board feet using nominal dimensions. Note that framing lumber like a 2x4 is usually priced per piece rather than per board foot, but the board-foot figure is still useful for comparing volume.