What is a board foot?
A board foot is 144 cubic inches of lumber (one foot square by one inch thick). It’s a volume, not a length. Hardwood is sold this way, always by nominal thickness, so a surfaced 4/4 board that measures 13/16 in still charges as a full inch.
How the lumber yard actually measures your boards
A hardwood grader doesn’t measure a board the way you’d measure a shelf. Width is taken at the narrowest point along the board between two sawn edges, wane excluded, then rounded to the nearest whole inch. A board running 6 1/4 in tallies as 6. One landing exactly on 6 1/2 is counted alternately up and down through the pack, so the rounding roughly evens out over a stack.
Length always rounds down to the whole foot, so 8 ft 7 in is tallied as 8. Those two figures give surface measure (width in inches times length in feet, divided by 12). Board feet is surface measure multiplied by the nominal thickness in inches, which is why a 4/4 board’s board footage and its surface measure come out as the same number.
The mistake that costs people money is measuring in the wrong places. Rough-sawn boards taper (saw a log and the edges are rarely parallel), so measuring the wide end can add half an inch of width the yard will never charge you for, and never credit you for either.
Measuring a surfaced board’s real thickness is the other one. 4/4 dresses to 13/16 in and 8/4 to 1 3/4 in, but both are charged at the nominal size, the full 1 in and the full 2 in.
Live-edge slabs are different again. The convention is average width, taken at three or four points along the length, not the width at the widest bulge. Any yard quoting off the bulge is quoting high.
Work from a cut list, not from the finished object. Write every part down at its finished size, convert each to board feet at the nominal thickness you intend to buy, and total it. A 36 × 72 in table top is 18 sq ft, so 18 board feet in 4/4.
None of that allows for the saw kerf between the boards you glue up, the trim off both ends, or the board you reject after opening it and finding a shake running through the middle. How much allowance you need depends on the grade you buy, which is the next thing to get right.
Thickness and grade: what to order
So what does 4/4 on the price board mean? Hardwood thickness is quoted in quarters of an inch of rough stock, and each size dresses to a published figure. 4/4 surfaces to 13/16 in, 5/4 to 1 1/16 in, 6/4 to 1 5/16 in and 8/4 to 1 3/4 in.
The practical rule is to buy at least one full step above your finished thickness whenever the board isn’t dead flat. A finished 3/4 in part out of 4/4 rough gives you a quarter of an inch to lose to cup, twist and snipe. The same part out of 13/16 in S2S leaves you a sixteenth, and any cup at all will have you planing down to 5/8 in to clean it up. Thicker stock also costs more per board foot, because fewer logs yield it.
Grade is a yield promise, and you can use it directly as a buying multiplier. Under the NHLA rules, FAS boards are a minimum of 6 in wide and 8 ft long and must yield 83 1/3% clear face cuttings. Selects drop the minimum board to 4 in × 6 ft.
No. 1 Common is 3 in × 4 ft minimum and yields 66 2/3%, and No. 2A Common yields 50%. Those yields are where the multiplier comes from.
So if your cut list totals 40 board feet of finished parts, order roughly 48 in FAS and closer to 60 in No. 1 Common, then add your own cutting waste on top of that. Narrow parts (rails, stiles, drawer sides, legs) usually come out of No. 1 Common cheaply. Wide, continuous, uninterrupted surfaces want FAS.
Moisture is the last variable. Get it wrong and it ruins finished work. Kiln-dried hardwood for interior use leaves the kiln at 6–8% moisture content, which is about right for a heated house. Air-dried stock sits nearer 12% and will keep moving after you’ve glued it up.
Sticker the boards flat with spacers between them, in the room the piece will live in, for a week or two before you mill anything. Take the thickness off in two passes a day apart, so the movement that surfacing releases happens before your final dimension rather than after it. Add 10–15% beyond the standard waste allowance if you’re matching grain across a panel.
What it costs, and when board feet is the wrong unit
Retail hardwood prices spread widely by species, region and yard. Treat any published figure as a starting point and check with your local supplier before you budget. The ranking is fairly stable even when the numbers aren’t. Poplar is the cheapest of the common cabinet woods, ash and red oak sit a step above it, cherry and hard maple above that, white oak higher again, and walnut usually two to three times the price of poplar.
Most yards run volume tiers that take a fixed amount off the board-foot rate at 20, 50 and 100 board feet. Rounding an order up to reach the next tier only pays when the discount step is large. On a step of a few tens of cents, the extra board feet cost more than the deeper discount saves, so do the arithmetic both ways before you add to the order.
Surfacing costs more again, S4S more than S2S, and thicker stock carries a premium per board foot rather than a flat premium per piece. Prices here are US dollars, as of mid-2026. Canadian yards such as A&M Wood Specialty, KJP Select Hardwoods and Windsor Plywood sell by the board foot too, and quotes there run roughly 1.3–1.5× these figures in CAD.
Whether to buy rough or surfaced comes down to whether you own a jointer and a planer. If you do, buy rough. You keep the extra thickness, you see the grain after your own first pass, and you pay less. If you don’t, buy S2S and design your parts around 13/16 in rather than fighting for 3/4 in.
Skip-planed stock is the middle ground (enough surfacing to read the figure and color, not enough to give the thickness away). Straight-line ripping is usually worth paying for on anything over 8 ft, because a bowed edge fed against a table-saw fence is how good boards get ruined.
Ask before ordering whether the yard tallies at nominal size, or whether it applies a milling allowance when it surfaces the boards for you.
Board feet is the right unit for rough and thickness-milled hardwood, and the wrong unit almost everywhere else. Softwood framing is sold by the piece or the linear foot. A 2×4×8 tallies 5.33 board feet at nominal size but only 3.5 at its actual dressed 1 1/2 × 3 1/2 in, and no lumberyard prices it either way.
Sheet goods go by the sheet, a 4 × 8 panel being 32 sq ft. Moldings, pre-dimensioned S4S stock and flooring sell by the linear or square foot. Turning blanks and bowl squares sell by the piece. Use this calculator when the price tag says per bd ft, and the vendor’s own unit when it doesn’t.
Common questions
How do I read 4/4 and 8/4?
Quarters of an inch of nominal rough thickness, so 4/4 is one inch and 8/4 is two. Surfaced boards measure less once they’re planed, but they still price at the nominal size.
Is a board foot the same as a linear foot?
No. A linear foot is just length along the board and ignores width and thickness. A board foot is a volume (144 cubic inches), so the same 8 ft board can be 4 or 16 board feet depending on its section.
How much extra should I buy?
Add about 15–20% for defects, snipe and end trim. Go higher if you’re working around knots or matching grain across a panel, where sound boards get rejected just for looking wrong.
How many board feet is a 2x4x8?
At nominal size, 5.33 board feet (2 × 4 × 96 in divided by 144). At its actual dressed size of 1 1/2 × 3 1/2 in it’s only 3.5. Framing lumber is priced by the stick or the linear foot, so the board-foot figure is really only useful when you’re comparing softwood against hardwood on a like-for-like basis.
Why did the lumber yard tally more board feet than I measured?
Usually one of three reasons, all legitimate. Thickness is charged at the nominal size, so a surfaced 13/16 in board bills as a full inch. Widths round to the nearest inch, and exact half-inches alternate up and down through a pack. And some yards add a milling allowance to the tally when they surface. Ask which of the three applies, and what the allowance is.
How do I convert board feet to square feet?
Only at a stated thickness. Divide board feet by the nominal thickness in inches. 40 board feet of 4/4 covers 40 sq ft, the same 40 board feet in 8/4 covers 20, and in 5/4 about 32. So any coverage figure quoted without a thickness attached is meaningless (always ask which quarter it refers to).
Should I buy rough or S2S lumber?
Rough if you have a jointer and a thickness planer, since you keep the full thickness and pay less per board foot. S2S if you don’t, accepting that 4/4 arrives at 13/16 in and every part has to be designed around that. Skip-planed is the compromise. Enough is cleaned up to read the grain and color, with the thickness left on.
How much extra should I buy for a glue-up panel?
Beyond the usual 15–20% for defects and end trim, add another 10–15% when the panel has to match for grain and color, because you’ll reject boards that are perfectly sound but simply wrong-looking. Buying every board for one panel from a single pack, ideally consecutive off the same log, usually cuts that rejection rate sharply.