| Thickness (in) | Width (in) | Length (in) | Qty | Board feet |
|---|
How to calculate board feet
A board foot is 144 cubic inches: one foot square, one inch thick. The arithmetic follows straight from that.
thickness (in) x width (in) x length (in) / 144
If the length is in feet, divide by 12 instead of 144 - it is the same sum with the twelve already taken out of the length:
thickness (in) x width (in) x length (ft) / 12
A 1 inch by 6 inch board, eight feet long: 1 x 6 x 96 / 144 = 4 board feet. A stack of ten of them is 40.
Two details decide whether your number matches the yard's ticket. The first is which thickness goes in. Hardwood is measured rough, before surfacing, so a 4/4 board counts as a full inch even though it planes down to 13/16. Construction lumber is the other way round: a 2x4 is figured at its nominal 2 by 4, not its actual 1.5 by 3.5, which is why a 2x4x8 comes to 5.33 bf rather than 3.5.
The second is how a rough board is tallied, and the rule is not the one most people assume. Under the NHLA rules the trade grades by, width rounds to the nearest whole inch and length rounds down to the whole foot: a board 5 1/4 inches wide and 8 1/2 feet long is tallied as 5 inches and 8 feet. Widths landing exactly on the half inch are rounded up and down alternately, and the width taken is the average across the board, excluding wane.
The two roundings are not the same kind of rule. Width goes to the nearest inch, which is even-handed and averages out across a pile. Length always goes down, which never favours you: 8 feet 11 inches is tallied as 8 feet. So expect your own figure to run a little above the ticket on long boards, and calculate it beforehand not to predict the ticket to the penny but to know when the ticket is wrong.
The quarter system: 4/4, 5/4, 8/4
Hardwood thickness is quoted in quarters of an inch, and the number is the rough thickness.
| Quarter | Rough | Typical surfaced (S2S) | What it is for |
|---|---|---|---|
| 4/4 | 1" | 13/16" or 3/4" | Most furniture parts, shelving, drawer sides |
| 5/4 | 1 1/4" | 1 1/16" | A full inch after planing, stair treads |
| 6/4 | 1 1/2" | 1 5/16" | Table aprons, thick door stiles |
| 8/4 | 2" | 1 3/4" | Legs, workbench tops, chair parts |
| 12/4 | 3" | 2 3/4" | Turning stock, heavy legs |
| 16/4 | 4" | 3 3/4" | Large turnings, timber-scale parts |
Two consequences that cost money. The tally is taken on the rough measure, so you pay for the full 4/4 or 8/4 whether or not the finished part uses it - ordering 8/4 for a part that finishes at 3/4 buys you twice the wood you need. (Surfacing, when the dealer does it, is billed as work on top of that rough tally rather than folded into a thinner measurement.) And a part that must be a full inch thick after planing needs 5/4, not 4/4 - a mistake that only shows up after the boards are home.
Board feet, square feet and linear feet
Three different questions, and the words get used as if they were interchangeable.
| Measure | What it counts | Formula | Sold this way |
|---|---|---|---|
| Board foot | Volume | thickness (in) x width (in) x length (ft) / 12 | Rough hardwood |
| Square foot | Area | width (ft) x length (ft) | Sheet goods, flooring, veneer |
| Linear foot | Length only | total length (in) / 12 | Trim, moulding, deck boards, pipe |
Board feet and square feet meet through thickness, which is what makes the conversion feel slippery. One board foot of 4/4 covers a square foot; one board foot of 8/4 covers half of one, because the same volume is spread half as far. To go from board feet to square feet, divide by the thickness in inches. To go back, multiply by it.
That conversion uses the nominal thickness, which is the right one for buying. Surfaced boards cover a little more than it predicts - a 4/4 board planed to 13/16 spreads each purchased board foot over about 1.2 square feet - so do not be surprised when the finished panel measures larger than the arithmetic said.
Linear feet ignore both width and thickness, so ten linear feet of 1x4 and ten linear feet of 1x12 are the same number and nothing like the same amount of wood. If that is the number you are after, the linear cut calculator works it out along with how many sticks to buy.
What a board foot costs
4/4 FAS, at a retail hardwood dealer, mid-2026:
| Species | Typical price per bf |
|---|---|
| Poplar | $4-6 |
| Soft maple, red oak, ash, cherry | $6-9 |
| Hard maple, white oak, sapele | $8-12 |
| Walnut | $12-18 |
| Genuine mahogany | $14-22 |
| Figured, quartersawn or imported stock | $15-40+ |
Treat these as the shape of the range rather than a quote: species, grade, thickness, width and how far the truck came all move the number, and it moves again every year. Put your own yard's price into the calculator.
Three things routinely surprise people at the till. Wide boards cost more per board foot than narrow ones of the same species, because they came from bigger logs - a wide-board premium of around 25% above about 11 inches is common, and published openly by dealers who charge it. Thicker stock costs more per board foot as well, for the same reason plus longer drying: the same red oak can run $6 in 4/4, $7.50 in 8/4 and over $14 in 12/4. And surfacing is billed as work on top of the rough tally, so a "surfaced two sides" price is not the price on the rack.
Rough boards, and why the estimate always runs short
Rough hardwood is sold as it comes off the mill: random widths, random lengths, one edge often unusable, ends checked. That is why every experienced buyer adds an allowance, and why this calculator has an overage field set to 15% out of the box.
Where the extra goes:
- Random widths. Your part list wants 5 inch pieces and the rack has 7 3/4 and 11 1/2 inch boards. The rip leaves a strip too narrow for anything on the list.
- Defects. Knots, checks and sapwood on the wrong face get cut out, and they are not evenly spread.
- Jointing and planing. Flattening a rough board takes thickness, and straightening an edge takes width.
- Trimming ends. The last few inches of a board are usually split.
Ten per cent is a lean allowance, and only defensible for simple parts out of clear FAS stock. Fifteen is the usual advice. Twenty-five to thirty is the honest figure for lower grades, for a first project, for figured wood, or for anything where the grain has to match across parts - on rough low-grade material a third of what you carry home can end up as offcut.
From board feet to a cut list
Board footage answers "how much wood do I buy". It does not answer "which parts come out of which board", and the second question is where the first one usually goes wrong: a list that needs 40 bf of wood does not fit in 40 bf of boards, because parts cannot span two boards and the drop at the end of each one is only useful if something on your list is shorter.
Once you know the species and thickness, put the actual part lengths into the linear cut calculator - it packs your parts onto standard stock lengths, subtracts the saw kerf between cuts, and reports how many boards to buy rather than how many board feet. For sheet goods the cutting optimizer does the same in two dimensions.
FAQ
What is a board foot?
A board foot is a unit of volume equal to 144 cubic inches - a piece one foot square and one inch thick. It is how hardwood is sold, because a rough board has no fixed width: two boards of the same board footage can be one wide plank or two narrow ones. A board foot is not a measure of area or of length.
How do I calculate board feet?
Multiply thickness in inches by width in inches by length in inches and divide by 144. If the length is in feet, multiply thickness by width by length in feet and divide by 12 instead - the same calculation. A 1 inch by 6 inch board eight feet long is 1 x 6 x 96 / 144 = 4 board feet.
How many board feet are in a 2x4x8?
5.33 board feet. Construction lumber is figured at its nominal size, so a 2x4 counts as 2 by 4 even though it measures 1.5 by 3.5 inches: 2 x 4 x 96 / 144 = 5.33. Hardwood is figured at its nominal thickness too - the difference is that in hardwood the nominal figure is the rough thickness, so 4/4 counts as a full inch even when the surfaced board in your hands measures 13/16.
What is the difference between board feet and square feet?
Board feet measure volume, square feet measure area, and the two only line up through thickness. One board foot of 4/4 stock covers one square foot; one board foot of 8/4 covers half a square foot, because the same volume is spread half as far. Divide board feet by the thickness in inches to get square feet.
Is 4/4 lumber really one inch thick?
It is one inch rough, before surfacing. Once both faces are planed, 4/4 usually measures 13/16 or 3/4 inch - but the tally is taken on the rough measure, so you still pay for the full 4/4 - surfacing is billed as work on top of it, not as a thinner board. Order 4/4 for a finished part that must be 3/4, and step up to 5/4 if you need a full inch after planing.
How much does a board foot cost?
In mid-2026, roughly $4-6 per board foot for poplar, $6-9 for soft maple, red oak, ash and cherry, $8-12 for hard maple, white oak and sapele, $12-18 for walnut and $14-22 for genuine mahogany, with figured and imported stock running to $40 and beyond. Those are 4/4 FAS at a retail dealer; thicker and wider stock costs more per board foot. Softwood is usually priced per piece or per linear foot rather than per board foot. Prices move; use your own yard's number in the calculator above.
Is the board foot calculator free?
Yes - free, no signup, no limit on rows. The cut list optimizer it links to is free as well.