Board Foot Calculator

What Is a Board Foot?

The unit measures volume, which is exactly why it survives in a trade whose goods arrive in random widths. A stack of oak with no two boards alike can still be priced on one number.

Hardwood is not sold by the piece. Walnut, maple and cherry come off the pile in whatever widths the log gave, and the dealer prices the lot per board foot — one rate covering a 6-inch board and an 11-inch one. Get the arithmetic wrong and a furniture project's lumber bill surprises you at the register; get it right and you can compare dealers, thicknesses and species on the same scale.

144 Cubic Inches, in Any Shape

Ohio State University Extension states it without hedging: the board foot is “defined as a piece of wood containing 144 cubic inches”, and “any piece of wood containing 144 cubic inches is a board foot (e.g., 3″ x 4″ x 12″; 2″ x 6″ x 12″; etc.)”.

That is why the panel prints a cubic-inch line under the headline. Enter 1 inch by 6 inches by 8 feet and it returns “4.00 board feet” with “Volume: 576 cubic inches” beneath — 4 × 144, exactly. The two lines are one quantity in two units, and the cubic-inch figure is the one to reach for when you are checking a board against a kiln load or a shipping crate rather than a price list.

• 12″ × 12″ × 1″ — the picture the name comes from.
• 6″ × 24″ × 1″ — half as wide, twice as long, same board foot.
• 3″ × 4″ × 12″ — a short stick of timber, still 144 cubic inches.

Thickness is the dimension that catches people out, because it is invisible from above. The same 6-inch-wide, 8-foot board returns 4.00 board feet at 1 inch thick and 8.00 at 2 inches, and on a hardwood invoice that is the whole difference between 4/4 and 8/4 stock.

Board Feet vs Linear Feet vs Square Feet

Three units, three different questions, and a lumber yard will quote you in all of them before lunch.

There is no conversion between them without the missing dimensions. An 8-foot board is 8 linear feet whether it is a 1×4 or a 2×12 — but it is 1.75 board feet in the first case and 11.25 in the second, more than six times the wood on identical footage.

Working in face area rather than volume — a floor, a wall, a countertop — starts in the Square Footage Calculator.

Which Lumber Is Actually Sold This Way

Hardwood is the board-foot trade. The American Hardwood Export Council publishes the same arithmetic this page uses — “W (width in inches) x L (length in feet) x D (thickness in inches) ÷ 12 = BF” — and the NHLA grading rules that set US hardwood prices are built on it.

Softwood construction lumber is usually tagged by the piece instead: a price for an 8-foot 2×4, not a rate per board foot. Board measure still runs the wholesale end of it, and there the American Softwood Lumber Standard defines the unit on nominal sizes, as “the nominal thickness in inches or fraction of an inch by the nominal width in feet by the length in feet”. That is why a mill quote in MBF — thousand board feet — will not agree with your tape measure.

Sheet goods stay out of it entirely. Plywood, MDF and melamine are sold by the sheet or the square foot, and running a 4×8 sheet through a board-foot formula produces a number nobody in that supply chain uses.

Pricing a floor rather than project lumber? The coverage math lives in the Flooring Calculator.

How Do You Calculate Board Feet?

One multiplication and one division. The divisor of 12 exists only because the length is in feet while the other two dimensions are in inches — nothing deeper than that.

The Board Foot Formula, Written Out

This is what the code does, in order:

bfEach = thickness (in) × width (in) × length (ft) ÷ 12
total  = bfEach × pieces

volume = total × 144            cubic inches
cost   = total × price          printed only when price is above 0

1 board foot = 144 cubic inches = a 12″ × 12″ × 1″ slab

The piece count is rounded to a whole number and never falls below one: 1.4 is treated as one piece, 1.5 as two, and a blank, a zero or a negative all become one.

Why the Divisor Is 12

Work in a single unit and the divisor is 144. A board 1 inch thick, 6 inches wide and 8 feet long is 96 inches long, so it holds 1 × 6 × 96 = 576 cubic inches, and 576 ÷ 144 = 4 board feet. Entering the length in feet folds the 12 inches per foot into the constant instead: 144 ÷ 12 = 12. Same answer, one conversion fewer, and the panel prints both halves of it — “4.00 board feet” and “Volume: 576 cubic inches”.

The middle line of the result shows the intermediate product rather than the volume: “Each piece: 1″ × 6″ × 8′ = 48 in²·ft ÷ 12”. Those 48 units are inches × inches × feet, which is why the label reads in²·ft and not cubic inches. Divide by 12 and you are at board feet.

Step by Step

• Measure thickness and width in inches and length in feet. Fractions go in as decimals — 0.75 for a surfaced 1× board, 1.5 for a 2×, 0.8125 for surfaced 4/4 hardwood.
• Decide which convention you are in before you type. Rough hardwood: use the quarter thickness the dealer bills. Surfaced softwood: the actual size tells you the wood you are getting, the nominal size reproduces the trade tally. The chart below carries both, and they are far apart.
• Enter the piece count for identical boards only. Anything of a different size is a separate run.
• Leave Price per Board Foot at 0 unless you have a real quote. The box arrives with 0 in it, and everything that is not a digit or a decimal point is stripped out, so “$4.50” and “4.50 USD” both read as 4.5.
• Press Calculate. Nothing recalculates as you type, and the three measurement boxes start empty, so the panel shows a dash until you press the button. Reset returns it to that state.

A thickness, width or length that is blank, zero, negative or not a number gets the amber notice instead of a result. Above zero nothing is refused: the boxes carry no minimum and no maximum, so 0.0625 inch and a 1,000-foot length both calculate quite happily.

Worked Example: 8/4 Maple, 8 Inches Wide, 10 Feet Long

Thickness 2, width 8, length 10, one piece, price 8. Press Calculate and the panel reads:

• 13.33 board feet
• Each piece: 2″ × 8″ × 10′ = 160 in²·ft ÷ 12
• Volume: 1,920 cubic inches
• Cost at $8/bf: $106.67
• Use the lumber's ACTUAL dimensions (a 2×4 is really 1.5″ × 3.5″) — see the nominal-size table below

Trace it through: 2 × 8 × 10 = 160, and 160 ÷ 12 = 13.3333, displayed as 13.33. The cost line multiplies the unrounded 13.3333 by 8 to reach $106.67. Multiply the 13.33 on your screen by 8 instead and you get $106.64 — three cents adrift on one board, and more on a pallet.

That fifth line is fixed text. It prints on every result whatever you entered, and it is a warning about surfaced softwood rather than a comment on this maple, where the rough 2-inch thickness is precisely what the dealer bills.

Worked Example: Ten 2×4s, Actual vs Nominal

Ten 8-foot 2×4s at their real dimensions — thickness 1.5, width 3.5, length 8, ten pieces, price left at 0 — return four lines plus the fixed closing one:

• 35.00 board feet
• 10 pieces × 3.50 bf each
• Each piece: 1.5″ × 3.5″ × 8′ = 42 in²·ft ÷ 12
• Volume: 5,040 cubic inches

Now type the name instead of the measurement — thickness 2, width 4, same length and count — and the headline becomes “53.33 board feet” over “10 pieces × 5.33 bf each”. Identical sticks of wood, 18.33 board feet more on paper, because a dry 2×4 is dressed down to 1-1/2 by 3-1/2 inches.

That gap is 52%, and neither figure is a mistake. The nominal one is what the American Softwood Lumber Standard calls board measure; the actual one is the wood in your truck. Use the first to check an invoice quoted in board feet, the second to work out whether the load will yield your parts.

Doing It Without the Calculator

Three shortcuts fall straight out of the formula, and each is exact rather than approximate.

• 4/4 stock, 1 inch thick: board feet = width in inches × length in feet ÷ 12. A 6-inch board 8 feet long is 4.00.
• 8/4 stock, 2 inches thick: divide by 6 instead of 12. That same 6-inch board at 12 feet is 12.00 board feet.
• Any 2× softwood at 8 feet: the board feet equal the actual width in inches. A 2×8 measures 7.25 inches wide and returns 7.25 board feet; a 2×12 measures 11.25 and returns 11.25.

The third one is why the actual-size column in the chart below looks copied from the width column. It holds at 8 feet only, because 1.5 × 8 ÷ 12 comes to exactly 1.

Board Foot Chart

Three tables, every figure generated by running this calculator rather than copied from a chart somewhere else.

Nominal vs Actual Softwood, 8-Foot Pieces

Surfaced softwood is named for the size it was before drying and planing. What you get and what the name implies are two different numbers:

The actual sizes are not folklore. NIST's Voluntary Product Standard PS 20-20, the American Softwood Lumber Standard, sets minimum dressed dry widths of 3-1/2, 5-1/2, 7-1/4, 9-1/4 and 11-1/4 inches for nominal 4, 6, 8, 10 and 12, takes a nominal 1-inch board down to 3/4 inch dry, and states in its terminology section that “a dry 2 by 4 is surfaced to 38.1 mm by 88.9 mm (1 1/2 by 3 1/2 inches)”.

The gap narrows as boards get wider — 52% on a 2×4, 42% on a 2×12 — because the half inch lost off a 4-inch width is a bigger share than the three-quarters lost off 12. Green lumber is dressed larger still: PS 20 allows 25/32 inch for a green nominal 1-inch board and 5-5/8 inches for a green nominal 6 width, so the same nominal size holds more wood green than dry.

Hardwood Quarters: Board Feet in an 8-Foot Board

Rough hardwood is billed at these thicknesses. Find your width down the side, read across to the thickness the dealer quotes:

Every row scales cleanly: 8/4 is twice 4/4 and 12/4 is three times it, because thickness enters the formula once and nothing else moves. For another length, scale again — the same table at 10 feet is these figures times 1.25, which puts a 4/4 board 8 inches wide and 10 feet long at 6.67 board feet.

The Same Board at Every Standard Length

One 6-inch-wide board, two thicknesses, across the lengths a hardwood dealer stocks:

A 6-inch 4/4 board yields half its length in board feet, so that column is simply the length halved. It is a coincidence of the width rather than a rule — an 8-inch board at the same thickness runs two-thirds of its length, giving 8.00 board feet at 12 feet.

What Do 4/4, 6/4 and 8/4 Mean?

Quarters of an inch of rough thickness — and, more to the point, the thickness you are billed for.

The Quarter System

“Standard thickness for rough sawn lumber is expressed in quarters of an inch,” says the American Hardwood Export Council; “for example 1″ = 4/4.” The ladder runs 3/4 (19.0 mm), 4/4 (1″, 25.4 mm), 5/4 (1¼″, 31.8 mm), 6/4 (1½″, 38.1 mm), 8/4 (2″, 50.8 mm), 10/4 (2½″, 63.5 mm), 12/4 (3″, 76.2 mm) and 16/4 (4″, 101.6 mm), with most US hardwood production sawn between 1 and 2 inches.

They are spoken as “four-quarter” and “eight-quarter”, never as fractions. In the thickness box they go in as decimals: 1 for 4/4, 1.25 for 5/4, 1.5 for 6/4, 2 for 8/4.

Why You Pay for Wood That Was Planed Away

The rough thickness is billed even when the board has already been surfaced thinner. AHEC gives the planing allowance: “The finished thickness for lumber of 1 1/2″ and less can be determined by subtracting 3/16″ from the nominal thickness. For lumber 1 3/4″ and thicker, subtract 1/4″.” Surfaced 4/4 therefore lands at 13/16 inch, and surfaced 8/4 at 1-3/4.

Put both through the calculator. A 4/4 board 6 inches wide and 8 feet long is billed at 4.00 board feet. Enter its surfaced thickness instead — 0.8125 — and the same board returns “3.25 board feet” with “Volume: 468 cubic inches”. Three-quarters of a board foot, about 19% of what you paid for, left the mill as shavings.

This is convention rather than markup: the wood was there when the board was graded and tallied, and the planing is what makes it usable. It does mean the thickness you type depends on the question. Checking an invoice, use the rough quarter figure. Working out whether you have enough wood for a glue-up, measure the board you are holding.

Buying Allowance, and Which Tally You Are Quoted

• Figure the project in finished dimensions, then buy the next quarter up. A finished 1¾-inch table leg needs 8/4 stock, because 6/4 surfaces out at 1-5/16.
• Add 15% to 30% over the cut-list total. This is a shop rule of thumb rather than a published standard: it absorbs the knots, checks and wane the grade permits, plus grain matching, snipe and test cuts. Painted utility work sits at the bottom of that band, grain-matched or figured work at the top.
• Ask whether the tally is net or green. AHEC defines net tally as “the actual board feet of kiln dried lumber measured after kiln drying” and gross or green tally as the count taken before drying — on that basis “the buyer can expect to receive approximately 7% less board feet because of shrinkage in the kiln drying process”.
• Ask whether the quoted footage is before or after defect cutting, and whether the price covers surfacing or adds it per board foot.

On a 100 board foot order the difference between a green tally and a net tally is about 7 board feet — roughly the cushion most people believe they are adding when they round the order up.

How to Read Your Result

Four lines come back for a single piece and up to six once you add a quantity and a price. Here they are exactly as they print, from thickness 1, width 8, length 10, six pieces and a price of 6.50:

• “40.00 board feet” — the headline, and the figure a dealer prices.
• “6 pieces × 6.67 bf each” — present only when the count is above 1.
• “Each piece: 1″ × 8″ × 10′ = 80 in²·ft ÷ 12” — your entry read back with the arithmetic showing.
• “Volume: 5,760 cubic inches” — the same wood in cubic inches, at 144 to the board foot.
• “Cost at $6.5/bf: $260.00” — present only when the price is above 0.
• “Use the lumber's ACTUAL dimensions (a 2×4 is really 1.5″ × 3.5″) — see the nominal-size table below” — fixed text on every result.

The Cost Line

It prints only when the price box holds a number above zero, and it is computed from the unrounded total, so it can sit a cent or two away from the board feet on screen multiplied by your price. It also echoes the price as a plain number rather than as currency: type 4.50 and the label comes back as “Cost at $4.5/bf”, with the cost itself correct at $18.00 on a 4.00 board foot order.

Anything that is not a digit or a decimal point is stripped before the number is read, so “$4.50”, “4.50 USD” and “4.5” are one entry. Letters on their own leave the price at 0 and the cost line simply does not appear.

Where the Display Rounds

• The headline carries two decimals: 13.3333 board feet prints as 13.33.
• The per-piece figure is rounded too, but the total is not built from it — six pieces at 6.6667 give “40.00 board feet”, where the 6.67 on screen would have given 40.02.
• The middle line rounds its product to a whole number. Enter 1 by 6.5 by 8.5 and it reads “Each piece: 1″ × 6.5″ × 8.5′ = 55 in²·ft ÷ 12” while the headline says “4.60 board feet” — the true product is 55.25, and 55 ÷ 12 would come to 4.58.
• The cubic-inch line takes no decimals and adds a thousands separator, as in “Volume: 96,000 cubic inches”.

None of that rounding touches the calculation. Every line is drawn from the full-precision value, which is exactly why they sometimes refuse to divide neatly into each other on the page.

When You See the Amber Notice

A single guard covers the three measurements. Leave thickness, width or length blank, at zero, negative or non-numeric and the panel turns amber under “Check your inputs” with the message “Enter thickness, width, and length greater than zero”.

The piece count has no guard of its own. Blank, 0 and negative values all resolve to one piece, and fractions are rounded to the nearest whole board — 1.4 gives one, 1.5 gives two. Pressing Calculate with the count left empty is therefore a perfectly valid single-board run.

Limits: When Board Feet Do Not Apply

The formula is exact. What it is exact about is a rectangular solid of wood, and there are several places in the lumber trade where that is not what is being bought.

One Size at a Time

The boxes describe a single board. A cut list carrying three thicknesses is three runs, added on paper afterwards — there is no running total between runs and no way to enter a list of sizes.

For a bundle of identical stock the piece count does the work. Ten layers of 2-inch boards averaging 40 inches wide and 10 feet long — thickness 2, width 40, length 10, ten pieces — return “666.67 board feet”, which is the layer-by-layer estimating method AHEC sets out for a unit of lumber, against its own worked figure of 667 board feet.

The Trade's Tally Rounds. This Does Not.

Hardwood inspection works from surface measure — width in inches times length in feet divided by 12 — rounded to a whole number before the thickness is applied. Purdue Extension records the tie-break: when the fraction is exactly one half it “is rounded up one time and down the next time”. AHEC adds that when a bundle is tallied, widths are taken to the nearest whole inch while lengths are always rounded down to the whole foot.

AHEC's own example is a board 2 inches thick, 6¼ inches wide and 8 feet long. Its surface measure of 4.17 rounds to 4, so the tally is 8 board feet. Enter the true dimensions here and the panel returns “8.33 board feet”. Neither is wrong; they answer different questions. Widths round either way, but lengths only ever round down, so a tally tends to sit at or a little below the volume you can measure.

Do not expect an invoice to match this page to the decimal, then. Expect it to match within the rounding, and query it when it does not.

Board Feet in a Log Are an Estimate, Not a Measurement

The same unit is used for standing trees and logs, and there it stops being arithmetic. Ohio State University Extension: the board-foot volume of a tree or log “cannot be measured exactly but is estimated”, because the yield depends on how the log is bucked, the sizes sawn, the sawdust lost and the mill doing the work.

Rival log rules disagree by a wide margin on the same tree. A 20-inch-diameter oak with 2½ logs of merchantable height holds 260 board feet by the Doyle rule and 350 by the International 1/4-inch rule — 90 board feet apart, a third more from one table than the other. OSU notes that the International rule “is generally considered to be the best estimate of the amount of lumber that can actually be sawn from a tree or a log under optimum conditions”.

This calculator does none of that. Hand it a log's diameter and length and it returns the volume of a rectangular block of those dimensions, which is more wood than any sawmill will ever get out of something round.

What the Number Leaves Out

• Waste. Nothing is added for defects, snipe or grain matching — the 15% to 30% allowance is yours to add before you type.
• Kerf. Every cut turns wood into dust: a full-kerf blade is about an eighth of an inch, so one rip down a 10-foot 4/4 board costs roughly 0.1 board feet.
• Money beyond the wood. Delivery, surfacing charges, sales tax and yard minimums are all outside the cost line, which is board feet times your price and nothing else.
• Moisture. A board tallied green shrinks as it dries, and AHEC puts that at about 7% of the board feet.
• Weight. Board feet measure volume; what the load weighs depends on species and moisture content, and this page does not model either.

None of these are arguments against the figure. They are the reasons to treat it as the number the order starts from rather than the number it ends at.