How to Calculate Board Foot Measure

A board foot is 144 cubic inches of lumber, meaning 1 inch thick by 12 inches wide by 12 inches long, and you calculate it as thickness in inches × width in inches × length in feet ÷ 12. When all three measurements are in inches, divide by 144 instead. A 2x4x8 comes to 5⅓ board feet; a 1x6x8 comes to 4. The dimensions you feed that formula have to be the ones the seller bills by. Paragraph 16 of the National Hardwood Lumber Association's 2023 rulebook states that "in surfaced lumber, board footage is measured before surfacing," so a 4/4 board planed down to 13/16 inch is still charged as a full inch. Softwood graded under the U.S. Department of Commerce standard PS 20 is charged at nominal size, so a 2x4 that measures 1½ by 3½ inches is still billed as 2 by 4.

The sale basis decides your answer before the arithmetic does

There is one formula and at least five sets of numbers you could put into it: rough thickness, surfaced thickness, nominal size, actual measured size, or a log scale. Each one produces a mathematically defensible figure. One of them matches the quote in your hand.

I spent nine years auditing electricity bills for commercial charging depots, where this same problem wears a different costume. The meter records what left the transformer. The battery records what arrived. The invoice is written against one of those two numbers, and the depot manager who assumes it is the second one loses the argument every quarter. Nobody is lying; the gap has a name, and the name is the sale basis. Lumber behaves identically, except the gap is wider than most buyers guess, because a surfaced hardwood board is billed for wood that left the mill as planer shavings.

Get one sentence from the seller before you calculate anything: what thickness and width are you charging me for? A hardwood yard answers in rough quarters. A lumberyard selling framing answers nominal. A sawyer quoting logs names a log rule, and if he does not name one, what he gave you is not yet a number.

The volume definition, and why ÷12 and ÷144 are the same rule

The NHLA rules put it in one line: "One board foot is 12" wide by 12" long and 1" thick (144 cubic inches) or the equivalent." Board feet measure volume. That fact alone dissolves most of the confusion around this topic, since square feet measure area and linear feet measure length, and only volume carries thickness with it.

The two formulas circulating online are one equation in two costumes:

• thickness (in) × width (in) × length (ft) ÷ 12
• thickness (in) × width (in) × length (in) ÷ 144

The first divides by 12 because one dimension arrived in feet, and twelve of those inches are already baked into the 144. Feeding a length in inches into the ÷12 version overstates every board twelvefold, which is loud enough to catch immediately. The dangerous error is quieter: correct arithmetic, wrong dimensions.

How to tally one board

The NHLA method, condensed:

1. Measure width at the narrowest point within the standard length, on a sawn edge, keeping the fraction. Paragraph 10 of the rules fixes width at the narrow point.
2. Drop the length to the next lower standard length. Standard hardwood lengths run 4 through 16 feet in one-foot steps, so a board measuring 8 feet 4 inches tallies as 8 feet.
3. Calculate surface measure: actual width in inches × standard length in feet ÷ 12, rounded to the nearest whole foot. A result landing exactly on the half is counted alternately up, then down, on the next such board.
4. Multiply surface measure by rough thickness in inches. Thicknesses below 1 inch are measured as 1 inch under paragraph 16, so 1/2-inch stock still bills at a full inch of thickness.

Worked through: a rough 4/4 red oak board, 7¼ inches at its narrow point, 8 feet 4 inches long. Length drops to 8 feet. Surface measure is 7.25 × 8 ÷ 12 = 4.83, tallied as 5. At 4/4, board feet equal surface measure, so the board tallies 5 board feet against a true volume of 4.83.

Notice where the rounding sits. It lands on surface measure, before thickness enters. On 8/4 stock, every rounded half-foot of surface measure carries twice the volume and twice the money, which is why thick stock repays a recount.

Tallying a mixed pile without inflating it

Random-width hardwood is where per-board shortcuts go wrong. Six rough 4/4 red oak boards, each already trimmed to a standard length:

| Board | Width at narrow point | Standard length | Surface measure (raw) | Tallied SM | Board feet at 4/4 | |---|---|---|---|---|---| | 1 | 6¼" | 8' | 4.17 | 4 | 4 | | 2 | 7½" | 8' | 5.00 | 5 | 5 | | 3 | 9¾" | 10' | 8.13 | 8 | 8 | | 4 | 5½" | 12' | 5.50 | 6 (alternating turn) | 6 | | 5 | 8⅜" | 10' | 6.98 | 7 | 7 | | 6 | 11¼" | 12' | 11.25 | 11 | 11 |

True volume across the six boards is 41.02 board feet. The NHLA tally is 41. The alternating half-foot rule exists precisely so those roundings cancel across a pack, and over six boards it landed within two-hundredths of a board foot.

Now round each board up before adding, the way a price tag encourages: 5 + 5 + 9 + 6 + 7 + 12 = 44 board feet. At $4.50 per board foot, which is the published 4/4 red oak price at Country Concepts in Perkasie, Pennsylvania, checked in September 2026, the honest tally costs $184.50 and the rounded-up tally costs $198.00. That is $13.50 and 7.3 percent, on six boards.

A quarter of a board foot per board is the increment nobody disputes and everybody pays. It is the auditing equivalent of a door down the street that keeps opening and closing: you stop hearing it long before it stops happening.

Rough versus surfaced is where the real money hides

Hardwood thickness is quoted in quarters of an inch. Paragraph 14 of the NHLA rules sets standard surfaced thickness by subtracting 3/16 inch from rough thickness for stock 1½ inches and under, and 1/4 inch for stock between 1¾ and 4 inches:

| Rough | Surfaced two sides (S2S) | |---|---| | 4/4 (1") | 13/16" | | 5/4 (1¼") | 1-1/16" | | 6/4 (1½") | 1-5/16" | | 8/4 (2") | 1-3/4" |

Measure a surfaced 4/4 board and calculate from 13/16 inch, and you land on 81.25 percent of the billed figure. Take a 6-inch-wide, 8-foot 4/4 board: surface measure 4, billed as 4 board feet, $18.00 at the Country Concepts price. Calculated from its planed 13/16-inch face, the same board computes to 3.25 board feet and $14.63. You are 18.75 percent light on every single board.

Two related billing facts belong here. Rough thickness gets rounded to the nearest quarter for the tally, a practice hardwood dealers call the count, so ask which count a nominally 1-1/8-inch board is being sold on. And a yard's surfacing is usually a separate charge rather than a discount on the wood: Country Concepts bills machine surfacing at $85 per hour on top of the lumber.

Board feet, square feet, and log scales measure three different things

Here is why square footage and board footage get swapped so casually. At 4/4, they are numerically identical. Paragraph 18 states that random-width lumber is tallied by surface measure, and "this tally shall be the number of feet, board measure, of 1" lumber." A 6-inch by 8-foot board is 4 square feet and 4 board feet. Move to 8/4 and it is still 4 square feet, now 8 board feet. The two units agree at exactly one thickness and diverge everywhere else.

Flooring quotes ride in on this confusion. Flooring is sold by square feet of finished coverage, measured across the exposed face after the tongue has been milled away, so the square footage on a flooring invoice has already had the milling loss removed. Board footage on a lumber invoice has not. Converting between them requires the rough thickness the mill started from and the milling loss, and neither number appears on the flooring order.

Log rules answer a third question: how much lumber a sawyer can recover from a log after saw kerf and slabbing. Virginia Cooperative Extension publication 420-085 puts the three common rules side by side on 16-foot logs:

| Small-end diameter | International ¼-inch | Scribner Decimal C | Doyle | |---|---|---|---| | 12" | 95 bf | 80 bf | 64 bf | | 16" | 180 bf | 160 bf | 144 bf |

Doyle allows a 4-inch slabbing deduction and a 5/16-inch kerf, which is why it reads 33 percent below International on a 12-inch log and why sawyers describe recovering overrun against it. Applying any of these rules to boards already sawn imports a slab allowance that has physically already happened. The board in your hand has no kerf left to lose.

What the invoice is allowed to do, and what it is not

Rounding on the invoice is a commercial rule set by the seller, not a constant. Some yards bill exact tallies; others round each line up to the next whole board foot. That policy lives in the published price list or the written quote.

Two constraints are not the seller's to set. A model regulation adopted by the National Conference on Weights and Measures on July 21, 1977, and reprinted in the NHLA rulebook, requires that "sales of hardwood lumber measured after kiln drying shall be quoted, invoiced, and delivered on the basis of net board footage, with no addition of footage for kiln drying shrinkage." It is recognized as law in many states. If the lumber is measured green and dried afterward at your request, the kiln charge has to appear separately on the invoice. Buying kiln-dried lumber on a green tally means roughly 7 percent fewer board feet arrive than the tally claims, according to the American Hardwood Export Council's measurement guidance, which is a legitimate basis when stated and a quiet subsidy when not.

The second constraint is the tolerance. Section 8 of the NHLA Sales Code sets 4 percent of gross invoice money value as the threshold in a dispute inspection: come in at or under it and the buyer pays for the inspection and honors the invoice in full. That number is a useful audit trigger. The six-board example above came to 7.3 percent, which clears it. A single misread board rarely will.

When board feet are the wrong unit entirely

Plywood, MDF, and veneer sheets sell by the sheet or by the square foot, since their thickness is fixed and uniform. Mouldings, trim, and dowels sell by the linear foot, where width and thickness are set by the profile. Flooring sells by coverage. Standing timber sells by a log rule with the rule named. Reaching for board feet in any of those transactions produces a number that no invoice will recognize.

Careful measuring changes your tally, your order quantity, and your ability to challenge a line item. It cannot change which convention the yard sells under, and it will not retroactively convert a nominal quote into an actual one. Ask first, then measure.

Frequently asked questions

How many board feet is a 2x4x8?

An 8-foot 2x4 is 5⅓ board feet, calculated as 2 × 4 × 8 ÷ 12. That uses nominal size, which is how framing lumber is sold and invoiced. Measured at its actual dressed size of 1½ by 3½ inches, the same stud holds 3.5 board feet of wood, about 34 percent less than the billing figure.

How many board feet are in a 1x6x8?

Four board feet, from 1 × 6 × 8 ÷ 12 = 4, using nominal dimensions. The dressed board actually measures ¾ by 5½ inches, which computes to 2.75 board feet. Retailers price 1x6 stock at the nominal 4, so order against 4 and plan your cuts around 2.75 board feet of real material.

How many board feet are in a 2x3x10?

Five board feet: 2 × 3 × 10 ÷ 12 = 5. Under the American Softwood Lumber Standard, a dry 2x3 measures 1½ by 2½ inches, giving 3.125 board feet of wood. That 37.5 percent nominal-to-actual gap is wider than the 31.25 percent gap on a 2x6, because the half-inch loss eats a larger share of a 3-inch face.

How many board feet are in a 2x6x10?

Ten board feet, from 2 × 6 × 10 ÷ 12 = 10, one of the few sizes where the nominal arithmetic lands on a round number. The dressed board measures 1½ by 5½ inches and holds 6.875 board feet. You pay for 10 and build with just under 7.

How do I calculate board feet when length is in inches?

Divide by 144 rather than 12: thickness × width × length, all three in inches, ÷ 144. A board 1 inch thick, 7 inches wide and 90 inches long gives 1 × 7 × 90 ÷ 144 = 4.375 board feet. The 144 is simply the cubic-inch volume of one board foot, so the units cancel cleanly.

When should I use a log board-foot calculator instead?

Only when you are buying or selling logs, and only once the rule has been named in writing. Log rules estimate recoverable lumber after saw kerf and slab loss, so they answer a different question than a board tally. A 12-inch, 16-foot log scales 95 board feet on International ¼-inch and 64 on Doyle.