Board Foot Calculator — Lumber Is Billed on Dimensions the Board Does Not Have
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Calculate
This selector governs every field, label, result and export here, and it overrides the site header switch. The nominal softwood sizes and the hardwood quarter designations do not convert, because they are trade designations rather than measurements.
The Lumber
Asked first because it decides which dimensions the trade bills on. Softwood is billed on the nominal size. Hardwood is billed on the rough thickness before surfacing. The fields below follow from this answer.
The Length and the Count
It selects the divisor. Twelve with the length in feet and 144 with the length in inches are the same equation, and there is no default that is right across the four units.
In the unit chosen above, and not in the unit system selector. A metric length is converted to feet before the board foot equation runs, because the board foot is an Imperial trade unit.
A whole number of boards of this size. One board is an answer and is entered as 1. The count multiplies into the order total and the linear feet.
The Cut List (optional)
In the same length unit as the first entry, because a cut list is one order in one convention.
A whole number of boards of this second size.
In the same length unit as the first entry.
A whole number of boards of this third size.
The Order
Trade guidance puts approximately 7 percent between the two. Not stated is an answer: the page then reports both readings and applies neither, because it cannot tell whether your figure is gross or net.
As a percentage, reported on its own line and never folded into the board foot figure. Published guidance gives 15 percent as a starting point for figured or character grade hardwood.
In your own currency. Any cost shown is arithmetic on this figure and nothing else.
Per thousand board feet, which is the unit lumber is wholesale priced in. Enter one price or the other: a per board foot price and a per MBF price are a thousand apart.
Overview
A two by four eight feet long is billed as 5.333 board feet. The board in your hand holds 3.500. That is 52.4 percent more than the wood contains, and it is not a mistake.
A board foot is a foot long, a foot wide and an inch thick, and every calculator on the subject multiplies three numbers and divides by twelve. The arithmetic is not where this goes wrong.
Lumber is billed on dimensions the board does not have, and the trade does it two different ways depending on what wood you are buying.
Softwood is billed on the nominal size. Voluntary Product Standard PS 20-25 defines board measure in its own words: the number of board feet is obtained by multiplying the nominal thickness in inches by the nominal width in feet by the length in feet. The minimum dry dressed size the same standard sets for a nominal two by four is one and a half by three and a half, which is where the 3.500 comes from, and the gap read against the invoice rather than the board is 34.4 percent.
Hardwood is billed on the rough thickness before surfacing. The NHLA rules state that in surfaced lumber, board footage is measured before surfacing. A four quarter board is one inch rough, dresses to thirteen sixteenths under the standard surfaced thickness table, and is billed at the full inch. That is 23.1 percent more billed than carried home, or 18.75 percent of the billed thickness.
Neither is an error and neither matches a tape.
Then the roundings pull opposite ways on one board. Thickness rounds up to the next full quarter, so a board measuring one and seven eighths is billed as eight quarter. Length rounds down to the whole foot, so eight feet six inches is tallied at eight.
What to Look at First
Read the two figures side by side before you read either one alone. On softwood they are the nominal billed volume and the minimum dry dressed reference, and they differ by 52.4 percent on a two by four. On hardwood they are the trade tally from the rounded surface measure and the geometric volume from the three dimensions, and on the published example board they are 8 and 8.67. Neither pair is one number with an error in it: they answer different questions, and the invoice carries the first of each pair.
Then read the tally basis. It is the largest single correction on this page, it is worth about seven percent, and it is invisible on a quote that does not say which basis it used. Where the basis is not stated this page reports both readings and applies neither, because treating an unstated figure as gross would be assuming the answer.
The gap percentages always arrive in pairs with their bases named. The same gap on a two by four is 52.4 percent against what the board contains and 34.4 percent against what the invoice charges for, and a figure quoted without its base cannot be checked.
How to Use This Calculator
Say what wood you are buying before anything else. Softwood and hardwood are billed on different dimensions for different reasons, and applying one convention to the other produces a figure no invoice matches.
Say what unit the length is in. The same equation divides by twelve with feet and by 144 with inches, and a length in inches entered as feet is out by a factor of twelve rather than by a percentage.
Read the figures your route produces. Softwood gives a nominal billed volume and a dressed reference beside it. Hardwood gives a trade tally from the rounded surface measure and a geometric volume. A board you measure yourself gets the tally the hardwood rules would give it, named as that rather than as an invoice figure.
Enter a surfaced thickness if you have one. The page reports what you are billed for against what you carry home, on both bases, and it stops rather than computing if the dressed figure exceeds the rough one it came from.
Ask the yard which tally the quote is on. Net is measured after kiln drying and green before it, and a green tally arrives about seven percent light.
Measure a tapering board where the rules book says to. Paragraph 17 takes the width one third of the length from the narrow end for surface measure, and paragraph 10 takes the width of a piece at the narrowest point in the standard length with a sawn edge.
Inputs & Outputs
Inputs
Outputs
Board Foot Formula
There are three routes and each has its own billed figure. The lumber type selects one and the other two do not run.
Softwood billed, from the nominal size
bf_soft = nom_thick_in * nom_width_in * len_ft / 12
Hardwood surface measure
sm_sf = width_in * len_ft / 12
Hardwood tally, from the rounded surface measure
bf_trade = sm_rounded * quarter_thick_in
Quarter thickness to inches
quarter_thick_in = quarters / 4
Geometric volume, any route
bf_geom = act_thick_in * act_width_in * len_ft / 12
Geometric volume, length in inches
bf_geom = act_thick_in * act_width_in * len_in / 144
The gap, against the board
gap_board_pct = (bf_billed / bf_geom - 1) * 100
The gap, against the invoice
gap_inv_pct = (bf_billed - bf_geom) / bf_billed * 100
Several pieces of one size
bf_total = bf_billed * pieces
A cut list summed
bf_list = bf_total_1 + bf_total_2 + bf_total_3
Board feet with the waste allowance
bf_order = bf_list * (1 + waste_pct / 100)
Thousand board feet
mbf = bf_order / 1000
Cost from a price per board foot
cost = bf_order * price_bf
Cost from a price per MBF
cost = mbf * price_mbf
Linear feet in the list
lin_ft = len_ft * pieces
Net from a green tally
bf_net = bf_gross * 0.93
Unit conversions
One board foot is 144 cubic inches and 0.002359737 cubic metres. One inch is 25.4 mm, one foot is 0.3048 metres and one square foot is 0.09290304 square metres.
Softwood is billed from the nominal size directly and never passes through the surface measure. Surface measure is a hardwood grading quantity, and putting a two by four through it gives a surface measure of 2.667 rounding to 3, times 2 inches, or 6 board feet, against the 5.333 every invoice carries.
Hardwood is billed from the rounded surface measure multiplied by the quarter thickness, which is the tally a grade sheet and an invoice carry.
A board you measure yourself has no invoice figure behind it, because nothing about it has been declared to a trade convention. It gets a geometric volume from its three dimensions, and beside that the tally the hardwood rules would give it once the thickness has been rounded up to the next full quarter.
The billed figure named in the gap equations is whichever of the first two ran. On a board you measured, a gap appears only when you enter a surfaced thickness, because that is the only figure there is to compare the rough volume against.
The two geometric volume equations are one equation. A board foot is 144 cubic inches, so dividing by 12 with the length in feet and by 144 with the length in inches give the same answer. The page asks which unit the length is in because there is no default right for both.
The surface measure rounds to the nearest whole number before the thickness is applied, and it rounds on each board rather than across a lot. Rounding is a function rather than an arithmetic expression and is stated here rather than in the block. Three boards of 6.5 inches by 8 feet by 2 inches give a surface measure of 4.3333 each, rounding to 4, so 8 board feet a board and 24 in total. Summing the areas first gives 13.0000, rounding to 13 and 26 board feet, and that is not the tally.
The width is not rounded. It enters the surface measure carrying its fraction, and what rounds is the surface measure. NHLA paragraph 16 says so directly: surface measure is expressed in whole feet and rounded up or down to the nearest whole number when it is calculated.
The thickness rounding to the next full quarter belongs to the measured route. A reader selecting 4/4 from the hardwood list has nothing to round, because a list cannot fall between its own entries. A reader who mics 1-7/8 on a measured board is told it is called and billed as 8/4.
The length rounding belongs to the two routes the association rules govern. Paragraph 16 drops fractions of feet longer than the standard lengths to the next lower standard length, and paragraph 12 gives those as whole feet from 4 to 16. Softwood is billed on the length ordered under a standard that sets sizes rather than a tally, so the rule is named on that route and not applied to it.
One further rule sets a floor. Paragraph 16 calculates board feet from the surface measure times the standard thickness, except that standard thicknesses less than one inch are measured as one inch, so a board thinner than an inch is tallied at an inch.
On the hardwood route two figures come out and they answer different questions. The trade tally comes from the rounded surface measure and is what a tally sheet and an invoice carry. The geometric volume comes from the three dimensions and is the wood in the board. On a board 6.5 inches by 8 feet by 2 inches those are 8 and 8.67, and neither is an error in the other.
On the softwood route the two figures are the nominal billed volume and the minimum dry dressed reference volume, and no surface measure appears.
The gap is two figures because it has two bases. Against the board it is how much more you are billed than the board contains. Against the invoice it is what share of the charge is not in the board. On a two by four those are 52.4 and 34.4 percent, and a page giving one without its base leaves a reader unable to check it.
The surfacing gap is taken on the same width and the same unrounded length on both sides, so it carries the thickness difference alone and never absorbs the surface measure rounding as well. That is why a four quarter board dressing to thirteen sixteenths returns exactly 18.75 percent of the billed thickness on every width and every length.
The net from a green tally equation runs on a green basis and, on an unstated one, only to show what the figure would become if it were gross. A net basis takes no correction at all.
The three terms in the cut list equation are representative. The build sums as many entries as were added, and an entry with a field missing is named and left out rather than completed by the page.
Two Conventions, and Neither Is What the Board Measures
Every board foot calculator multiplies three numbers and divides by twelve. The arithmetic is trivial and the inputs are not.
Softwood is billed on the nominal size, and the standard says so itself. Voluntary Product Standard PS 20-25, the American Softwood Lumber Standard, defines board measure as the nominal thickness in inches multiplied by the nominal width in feet multiplied by the length in feet. A two by four eight feet long is 5.333 board feet on that definition. Table 3 of the same standard sets the minimum dry dressed size of a nominal two by four at one and a half by three and a half, which is 3.500 board feet.
That is 52.4 percent more than the dressed reference contains, or 34.4 percent of what is billed, and it is not an error. It is what the trade prices in, and a calculator returning 3.500 would disagree with every invoice.
The standard is careful about what it is. It states of itself that it is not intended to be used either as grading rules or as purchase specifications, so its sizes are a manufacturing convention rather than a contract, and the dressed figures are minimums rather than descriptions of any particular board.
Hardwood is billed on the rough thickness, and the rules book is equally direct: in surfaced lumber, board footage is measured before surfacing. The quarter system counts rough stock in quarter inches, four quarter being one inch and eight quarter being two.
Paragraph 14 of those rules then sets what arrives. Standard thickness for surfaced lumber is the rough thickness less three sixteenths of an inch for stock one and a half inches and under, and less a quarter of an inch for stock between one and three quarters and four inches. One inch rough is S2S to thirteen sixteenths. So you pay for one inch and carry home 0.8125. That is 18.75 percent of the billed thickness, and 23.1 percent more billed than carried.
That is not a trick. Milling genuinely consumes wood to flatten a board, and a rough board that is cupped from drying cannot give a flat full inch.
Two conventions, two gaps, two different reasons, and neither matches a tape. So this page reports the billed figure and the actual figure side by side on every route where both exist, because a reader who measures will find the difference and needs to see that the page already accounted for it.
The Roundings Pull Opposite Ways on One Board
Thickness rounds up. A board measuring one and seven eighths is called and billed as the next full quarter, which is eight quarter at two inches, rather than as seven and a half quarters. That is 6.7 percent more than the tape says.
Length rounds down. Paragraph 16 of the rules states that in standard length lumber any fractions of feet longer than the standard lengths are dropped to the next lower standard length, and paragraph 12 gives those standard lengths as whole feet from four to sixteen. So eight feet six inches is tallied as eight, which is 5.9 percent less than the tape says.
So on one board the thickness is rounded against the buyer and the length in their favour, and no single direction describes the tally. A calculator that rounded everything one way, or nothing at all, would disagree with the invoice in a way the reader could not trace.
The width is not rounded at all, and this page had that as an open question until the rules book answered it. Under board measure what rounds is the surface measure: paragraph 16 states that surface measure is expressed in whole feet and rounded up or down to the nearest whole number when it is calculated. The width enters that product carrying its fraction.
The rule that rounds widths to the nearest inch belongs to a different method. Paragraph 21 describes the tally on a twelve foot basis, also called the export tally, where fractions below the half inch are dropped, fractions above the half inch are counted to the next higher width, and a length correction is applied afterwards. That is where the published example of a board measuring five and a quarter inches and being written as five comes from.
Paragraph 16 then settles which method wins. Where a footage dispute is caused by the use of both measurement methods, the footage determined by board measure supersedes. So the tally on this page never rounds the width, and where the export tally would reach a different surface measure that second reading is reported beside the first rather than folded into it.
Grade Rests on the Surface Measure, Not on the Board Feet
This is the fact most readers do not have, and it explains a price list that otherwise looks arbitrary.
Surface measure is the face area of the board in square feet: the width in inches times the length in feet divided by twelve, rounded to the nearest whole number. Board feet are then that figure multiplied by the standard thickness, except that standard thicknesses less than one inch are measured as one inch.
The rule that matters is what the grade is judged on. Paragraph 37 of the rules sets out the cutting unit method: a cutting unit is one inch wide and one foot long, there are twelve cutting units in one foot of surface measure, and to determine the number of cutting units a grade requires, the surface measure is multiplied by the yield fraction. FAS is the ten twelfths yield, which is 83.33 percent, so the requirement is the surface measure multiplied by ten.
There is no thickness term anywhere in that requirement. So a four quarter board and an eight quarter board of the same face carry the same grade requirement, contain twice the wood, and cost twice as much. The thickness moves the price and does not move the grade.
The two routes to a board foot figure also disagree, because the surface measure is rounded before the thickness is applied. A board six and a half inches wide, eight feet long and two inches thick gives 8 board feet through surface measure and 8.67 by the direct equation. This page reports both and names which one the tally uses.
And the rounding happens on each board rather than across a lot. Paragraph 18 tallies a surface measure on each piece, so three of those boards are 24 board feet and not the 26 that summing the areas and rounding once would give.
A Quote Without Its Tally Basis Is About 7 Percent Uncertain
Net tally is the board feet measured after kiln drying. Gross or green tally is the board feet measured before it. Published trade guidance gives the consequence: where kiln dried lumber is sold on a green tally basis, the buyer can expect to receive approximately 7 percent less board feet, because the wood shrank between the two measurements.
That 7 percent is a rule of thumb about what arrives rather than an allowance anyone is entitled to add. The rules book is explicit that no such addition is made: when inspecting kiln dried lumber, National Inspectors will make no addition for estimated kiln shrinkage.
What the rules book does carry is a requirement to say which basis was used. It reproduces the Model State Regulation adopted by the National Conference on Weights and Measures in 1977, which specifies 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, and that sales measured prior to kiln drying shall be quoted, invoiced and delivered on net board footage before kiln drying with the kiln drying charge shown separately. That regulation is recognised as law in many states.
Seven percent is larger than most of the other corrections on this page and it is invisible on a quote that does not say which basis it used. So this page asks, offers not stated as an answer, and where the basis is green or unstated it reports both figures rather than one.
The published rules also permit lumber to arrive scant of its nominal size. Under the Standard Kiln Dried Rule, rough kiln dried lumber specified three eighths to one and three quarter inches thick may be one sixteenth scant of the nominal thickness, two inch and thicker may be one eighth scant, and the minimum widths mentioned in all grades may be a quarter inch scant. Those are allowances written into the rules rather than defects, and a reader measuring a delivery against a tape will find them.
This Page Counts Board Feet and Grades Nothing
FAS is the top grade under the published rules. It admits widths of six inches and wider and lengths of eight to sixteen feet, on pieces that will yield ten twelfths, which is 83 and a third percent, clear face cuttings, with the number of cuttings permitted rising with the surface measure. No. 1 Common admits a lower yield on a sliding scale from twelve twelfths at one foot of surface measure down to eight twelfths, which is 66 and two thirds percent, on larger boards.
This page names those and issues no grade.
Grading is an inspection. Paragraph 5 of the rules determines the grade from the poor side of the piece, and the poor side is itself found by grading each face independently and comparing them. The clear face percentage is then determined by measuring the clear cuttings in inches of width by feet of length to give cutting units.
None of that can be done from three dimensions typed into a form. A calculator that returned a grade would be inventing an inspection, and the figure it returned would travel into a purchase order.
What the page does instead is report the surface measure, which is the number the grade is judged on, and the cutting units FAS would require on it, so a reader holding a rules card can carry out the comparison themselves.
What Is a Board Foot Calculation
A board foot is a volume: a foot square and an inch thick, or 144 cubic inches. Working out how many are in a board is one multiplication and one division.
What makes the subject hard is that the dimensions the trade uses are not the dimensions of the board.
For softwood the billed size is the nominal one, which the board stopped having at the mill. The published standard sets minimum dressed sizes for dry and green lumber separately, so a nominal two by four has a dry dressed reference of one and a half by three and a half, and the board foot count that appears on an invoice uses the two and the four.
For hardwood the billed thickness is the rough one, before surfacing. The quarter system counts rough stock in quarter inches, and a four quarter board that dresses to thirteen sixteenths is still billed at a full inch, because the mill sawed an inch and the planer took the rest.
Then the tally applies roundings that pull in opposite directions on a single board, and the grade is judged on a different quantity again: the surface measure, which is the face area in square feet.
So a board foot calculation is not one number. It is the figure the invoice will carry, the volume the board actually holds, the difference between them with its base named, and the tally basis the quote was written on.
Key Facts
- A board foot is one foot long, one foot wide and one inch thick, which is 144 cubic inches.
- The published formula is the width in inches times the length in feet times the thickness in inches, divided by twelve. With the length in inches the divisor is 144, and the two are the same equation.
- Voluntary Product Standard PS 20-25 defines board measure as the nominal thickness in inches multiplied by the nominal width in feet multiplied by the length in feet, so a 2 by 4 at 8 feet is billed at 5.333 board feet.
- PS 20-25 Table 3 sets the minimum dry dressed size of a nominal 2 by 4 at 1-1/2 by 3-1/2, giving 3.500 board feet, so the billed figure is 52.4 percent more than the reference contains and 34.4 percent of the invoice is not in the wood.
- PS 20-25, the American Softwood Lumber Standard, is effective January 2025 and supersedes PS 20-20 Revision 1.
- That standard states of itself that it is not intended to be used either as grading rules or as purchase specifications, so its sizes are a manufacturing convention rather than a contract.
- It defines dry lumber as lumber of less than nominal 5 inch thickness seasoned or dried to a maximum moisture content of 19 percent, which is the split its dry and green size tables sit either side of.
- PS 20-25 gives its sizes in both millimetres and inches and states that the imperial values are the units of record for the purposes of the standard, with the metric values given for information and comparison only.
- The same standard defines cubic measurement from the dressed thickness and width rather than the nominal, so a cubic metre figure taken on a piece is a different quantity from its board foot count converted.
- Hardwood thickness is expressed in quarters of an inch and the quarter figure is the rough thickness before milling: 4/4 is 1 inch, 5/4 is 1.25, 6/4 is 1.5 and 8/4 is 2.
- NHLA paragraph 16 states that in surfaced lumber, board footage is measured before surfacing, which is why the buyer is billed on the rough thickness.
- NHLA paragraph 14 sets standard surfaced thickness by subtracting 3/16 inch from rough stock 1-1/2 inches and under and 1/4 inch from stock between 1-3/4 and 4 inches, so 1 inch rough is S2S to 13/16.
- Paying for 1 inch and carrying home 0.8125 is 18.75 percent of the billed thickness, or 23.1 percent more billed than carried home, and milling genuinely consumes wood to flatten a board.
- Thickness rounds up to the next full quarter: a board measuring 1-7/8 inches is called and billed as 8/4.
- NHLA paragraph 16 drops fractions of feet longer than the standard lengths to the next lower standard length, and paragraph 12 gives standard lengths as whole feet from 4 to 16, so a board 8 feet 6 inches long is tallied at 8 feet.
- Surface measure is the width in inches times the length in feet divided by twelve, and NHLA paragraph 16 expresses it in whole feet rounded up or down to the nearest whole number when it is calculated.
- Board feet are then that figure times the standard thickness, except that standard thicknesses less than 1 inch are measured as 1 inch.
- The width is not rounded under board measure. The rule that rounds widths to the nearest inch belongs to the tally on a 12 foot basis in NHLA paragraph 21, and paragraph 16 states that where the two methods disagree, the footage determined by board measure supersedes.
- NHLA paragraph 37 puts 12 cutting units in one foot of surface measure and finds the units a grade requires by multiplying the surface measure, so FAS at the 10/12 yield of 83.33 percent requires the surface measure times ten.
- That requirement carries no thickness term, so all boards are graded the same way regardless of thickness and a 4/4 and an 8/4 board of the same face are graded identically.
- A board 6.5 inches wide, 8 feet long and 2 inches thick is 8 board feet by surface measure and 8.67 by the direct equation, because the surface measure rounds first.
- NHLA paragraph 18 tallies a surface measure on each piece, so three of those boards are 24 board feet rather than the 26 that summing the areas and rounding once would give.
- FAS admits widths of 6 inches and wider and lengths of 8 to 16 feet, on pieces yielding 10/12 clear face cuttings, from NHLA paragraphs 53, 54 and 62.
- NHLA paragraph 5 determines the grade from the poor side of the piece, which is why a grade cannot be issued from three typed dimensions.
- Net tally is the board feet measured after kiln drying and gross or green tally is the board feet measured before it, and trade guidance puts kiln dried lumber sold on a green tally at approximately 7 percent less board feet.
- That 7 percent is a rule of thumb about what arrives rather than a published allowance: the rules book states that National Inspectors will make no addition for estimated kiln shrinkage.
- The Model State Regulation reproduced in the rules book requires sales measured after kiln drying to be quoted, invoiced and delivered on net board footage with no addition for shrinkage, and sales measured before drying to be quoted on net board footage before drying with the kiln drying charge shown separately.
- Under the Standard Kiln Dried Rule, rough kiln dried lumber specified 3/8 to 1-3/4 inches thick may be 1/16 inch scant of the nominal thickness, 2 inch and thicker may be 1/8 inch scant, and the minimum widths mentioned in all grades may be 1/4 inch scant.
- NHLA paragraph 17 measures tapering lumber in standard lengths one third of the length from the narrow end for surface measure, and paragraph 10 takes the width of a piece at the narrowest point in the standard length with a sawn edge.
- Lumber is wholesale priced per MBF, a thousand board feet, which is the unit quotes are compared on, and one MBF is 2.36 cubic metres.
- Published guidance gives 15 percent as a starting point for figured or character grade hardwood, and notes that FAS rough sawn at 15 percent is a different proposition from No. 2 Common with knots throughout.
Applications
- Someone comparing a quote against a tape measure finds out why the two disagree and by exactly how much.
- A woodworker buying 4/4 for the first time learns that the 13/16 that arrives is the standard surfaced thickness rather than a short delivery.
- A reader with a cut list gets the total in the unit the yard prices in, alongside the linear feet the yard may quote instead.
- Someone with a quote in MBF converts it to compare against a per board foot price.
- A buyer asks which tally the quote uses, having found that a green tally arrives about seven percent light.
- A reader looking at a price list works out why a 4/4 and an 8/4 board of the same face carry the same grade and twice the price.
- Someone measuring a tapering board finds the two rules the rules book gives for which width to use.
- A reader ordering softwood sees the nominal figure the invoice will carry and the minimum dry dressed reference beside it.
Example Calculations
Example 1. The board and the invoice do not agree, by design
Given: a nominal 2 by 4, 8 feet long, one piece.
Billed on the nominal size, which is how PS 20-25 defines board measure: 2 times 4 times 8 divided by 12 is 5.333 board feet.
The minimum dry dressed size under PS 20-25 Table 3 is 1.5 by 3.5, which gives 1.5 times 3.5 times 8 divided by 12, or 3.500 board feet.
Result: 5.333 billed against 3.500 in the dressed reference. That is 52.4 percent more than the reference contains, and 34.4 percent of what the invoice charges for is not in the wood.
Neither figure is wrong. The nominal size is what the trade prices in, and a calculator returning 3.500 would disagree with every invoice in the yard. The dressed figure is a minimum the standard permits rather than a measurement of your board, which is why a board you measured yourself belongs on the measured route.
Example 2. Four quarter, and what arrives
Given: a 4/4 hardwood board, 6 inches wide, 8 feet long, surfaced on two sides.
Billed on the rough thickness of 1 inch: the surface measure is 6 times 8 divided by 12, which is 4 exactly, and 4 times 1 inch is 4.000 board feet.
The board arrives at 13/16, which is 0.8125 inches, from the standard surfaced thickness table. That is 0.8125 times 6 times 8 divided by 12, or 3.250 board feet.
Result: 4.000 billed against 3.250 carried home, which is 23.1 percent more billed than the board contains and 18.75 percent of the billed thickness.
The mill sawed a full inch and the planer removed the rest to flatten a board that came out of the kiln cupped. NHLA paragraph 14 subtracts 3/16 inch from rough stock 1-1/2 inches and under, which is where the 13/16 comes from.
Example 3. Two roundings, opposite ways, one board
Given: a board measuring 1-7/8 inches thick, 5-1/4 inches wide and 8 feet 6 inches long, entered on the measured route.
The thickness rounds up to the next full quarter, so it is called and billed as 8/4, which is 2 inches. That is 6.7 percent more than the tape says.
The length rounds down to the whole foot, so it is tallied at 8 feet. That is 5.9 percent less than the tape says.
The width is not rounded. It enters the surface measure at 5.25.
Result: the tally uses 2 inches, 5.25 inches and 8 feet. The surface measure is 5.25 times 8 divided by 12, which is 3.50 and rounds to 4, so the trade tally is 4 times 2, or 8 board feet.
The geometric volume on the same board is 1.875 times 5.25 times 8.5 divided by 12, or 6.97 board feet. The tally and the wood are different numbers and the invoice carries the first.
This is also the board the published example is worked on, and it is where the export tally shows its difference: under the twelve foot basis of NHLA paragraph 21 the width would be written as 5 inches, reaching a surface measure of 3 rather than 4. Paragraph 16 gives board measure precedence, so the page reports 4 and names the other reading beside it.
Example 4. Three boards, and where the rounding happens
Given: three boards, each 6.5 inches wide, 8 feet long and 2 inches thick.
Each board has a surface measure of 6.5 times 8 divided by 12, which is 4.3333 and rounds to 4. At 2 inches thick that is 8 board feet a board.
Three boards is 24 board feet.
Summing the areas first gives 13.0000, which rounds to 13, and 26 board feet.
Result: 24, not 26. NHLA paragraph 18 tallies a surface measure on each piece, so the rounding happens per board and never across a lot. The geometric volume on the three is 26.00, which is a third figure again and is not the tally.
Example 5. A quote with no tally basis
Given: a quote for 1,000 board feet of kiln dried hardwood, with the basis not stated.
If the quote is on a green tally, the board feet were measured before drying and the wood has shrunk since. Published guidance puts the difference at approximately 7 percent, so about 930 board feet would arrive.
If the quote is already a net tally, measured after drying, no correction applies and 1,000 arrive.
Result: two readings, not one. This page reports both and applies neither, because it does not know which basis the quote used and treating an unstated figure as gross would be assuming the answer.
That is 70 board feet of difference on one quote, which is larger than any other correction on this page. It is also why the Model State Regulation the rules book reproduces requires the basis to be identified on the quotation and the invoice.
Standards & References
- NIST Voluntary Product Standard PS 20-25, American Softwood Lumber Standard The current edition, effective January 2025 and superseding PS 20-20 Revision 1. Section 2.2 defines board measure on the nominal thickness and width, Table 3 sets the nominal and minimum dressed sizes for boards, dimension and timbers separately for dry and green lumber, and section 2.7 defines dry lumber at a maximum 19 percent moisture content.
- NHLA Rules for the Measurement and Inspection of Hardwood and Cypress The association rules book behind every hardwood figure here. Paragraph 12 gives the standard lengths, 13 the standard rough thicknesses, 14 the standard surfaced thicknesses, 16 the board foot and surface measure definitions with their rounding and the precedence of board measure, 17 and 10 the width of a tapering piece, 18 the per piece tally, 21 the tally on a 12 foot basis, 37 the cutting unit method, 5 the poor face rule, 53 to 62 FAS and 74 No. 1 Common. The Standard Kiln Dried Rule carries the scant allowances and the Model State Regulation on tally basis.
- National Hardwood Lumber Association The association that established the quarter thickness system and publishes and maintains the grading rules the surface measure, tally and grade figures on this page come from.
- American Lumber Standard Committee The standing committee responsible for maintaining the American Softwood Lumber Standard and for the accreditation programme behind softwood grade marks.
- AHEC, Grading sawn lumber, Measurement The published trade guide to the association measurement rules, and the source of the board foot definition quoted here, the surface measure formula, the quarter thickness list and the approximate 7 percent between a net and a green tally.
- NIST Voluntary Product Standards Program The programme under which the softwood lumber standard is developed and published.
- USDA Forest Products Laboratory, Wood Handbook The reference on wood properties, moisture content and shrinkage behind the difference between a green and a net tally.
- NIST Special Publication 811, Guide for the Use of the International System of Units The authority for the conversion factors used on this page.
The softwood figures on this page come from Voluntary Product Standard PS 20-25, effective January 2025 and superseding PS 20-20 Revision 1, and the edition is named because the tables change between editions. That standard sets minimum dressed sizes rather than describing any particular board, and it states of itself that it is not intended to be used either as grading rules or as purchase specifications, so the dressed figure here is a reference rather than a measurement: a reader who measures their own board should enter it on the measured route. The standard gives sizes in millimetres and inches and states that the imperial values are the units of record with the metric given for information and comparison only, which is why the nominal sizes and the quarter designations on this page do not convert.
The hardwood figures come from the NHLA rules book itself rather than from a trade summary of it, and three questions this page previously left open are closed by it. The surface measure is rounded to the nearest whole number and the width is not rounded at all under board measure; the rule that rounds widths to the nearest inch belongs to the separate tally on a twelve foot basis, and the rules book gives board measure precedence where the two methods disagree. The standard surfaced thicknesses, including thirteen sixteenths for four quarter, are a published table rather than an approximation. And the scant allowances are the Standard Kiln Dried Rule.
The approximate 7 percent between a green and a net tally remains trade guidance and is stated as approximate. It is a rule of thumb about what arrives rather than a published allowance, and the rules book is explicit that National Inspectors make no addition for estimated kiln shrinkage. The waste starting point of 15 percent is trade guidance and depends on a grade this page does not ask for.
This page counts board feet and issues no grade, because grading is an inspection of the poor face against published cutting rules that cannot be carried out from three typed dimensions.
Units
Board feet are reported with cubic metres alongside at 0.002359737, because a board foot is 144 cubic inches. One board foot is 0.00236 cubic metres and a thousand board feet is 2.36. That conversion is applied to the board foot figure the page computed; PS 20-25 defines its own cubic measurement from the dressed thickness and width instead, so the standard's cubic figure for a piece is a different quantity rather than this one restated.
Thicknesses and widths are in inches with millimetres alongside at 25.4. A 4/4 thickness of 1 inch is 25.4 mm, 13/16 is 20.64 mm and a 2 inch 8/4 is 50.8 mm.
Lengths are in feet with metres alongside at 0.3048. Eight feet is 2.438 metres.
Surface measure is in square feet with square metres alongside at 0.09290304. A surface measure of 4 is 0.372 square metres.
The nominal softwood sizes and the hardwood quarter designations do not convert. A two by four is a two by four and a 4/4 is a 4/4 in both unit systems, because they are trade designations rather than measurements. PS 20-25 takes the same position, giving its sizes in both units and stating that the imperial values are the units of record while the metric are given for information and comparison only.
Metric lumber is a different product list rather than a conversion of this one, and it is not modelled here.
The length carries its own unit selector rather than following the unit system, because the divisor follows the length unit and a reader may hold a metric tape and an imperial order. In metric mode a measured board is entered in millimetres for width, thickness and surfaced thickness. The length is converted to feet before the board foot equation runs, because the board foot is an Imperial trade unit.
The piece count, the surface measure once rounded, the waste percentage, both gap percentages and a price per board foot are dimensionless or unit free and are identical in both systems.
The internal unit selector governs the fields, labels, math, on-screen result and any exported result, and it takes priority over any site-wide unit switch. Switching converts the values you entered rather than reinterpreting them.
Limitations
- This page reports quantities and issues no pass or fail. The published figures are a manufacturing standard and grading association rules rather than limits.
- It does not grade a board. NHLA paragraph 5 determines the grade from the poor side of the piece, measured as clear cuttings in inches of width by feet of length to give cutting units, and that inspection cannot be done from three typed dimensions.
- It reports the cutting units FAS would require on your surface measure as published arithmetic. That is a requirement being named and not a grade being issued.
- It does not report a species, a moisture content or a drying schedule.
- The softwood reference is the minimum dry dressed table. PS 20-25 sets green dressed sizes separately, and this page names them without computing on them.
- The softwood dressed figures are the standard's minimums rather than measurements of any particular board, and the standard states it is not intended as grading rules or purchase specifications.
- It does not compute a span or a load, which is a different discipline with its own standards.
- It applies no correction to a tally basis that was not stated, because it cannot tell whether the figure given is gross or net.
- The 7 percent between a green and a net tally is one published approximate figure and a rule of thumb about what arrives, not an allowance written into the rules.
- Where a surface measure falls exactly on the half, the rules book counts pieces alternately to the next higher or lower foot across a lot. This page rounds a half away from zero and reports the other reading, because the alternation depends on the pieces tallied before yours.
- The 15 percent waste figure is a starting point for figured or character grade stock and never a threshold, because the grade that would justify moving it is not an input here.
- The cut list takes three entries. An entry with a field missing is named and left out of every total rather than completed by the page.
- It does not model metric lumber sizes, which are a different product list.
- It does not model log scales such as Doyle and Scribner, which are different rules for a different product.
- Any cost is arithmetic on a price you entered, in your own currency.
Common Mistakes to Avoid
- Entering a length in inches on the feet route. The divisor changes from 12 to 144 and the result is out by a factor of twelve.
- Using the dressed size for softwood. The invoice uses the nominal size, so a 2 by 4 at 8 feet is billed as 5.333 board feet and not 3.500.
- Using the surfaced thickness for hardwood. The billed thickness is the rough one, so a 4/4 board is billed at 1 inch even though it arrives at 13/16.
- Putting a softwood board through the surface measure. Surface measure is a hardwood grading quantity, and a 2 by 4 through it gives 6 board feet against the 5.333 every invoice carries.
- Applying one convention to the other wood. Softwood bills on nominal and hardwood on rough, for different reasons, and swapping them produces a figure no invoice matches.
- Quoting a gap percentage without its base. On a 2 by 4 the same gap is 52.4 percent against the board and 34.4 percent against the invoice.
- Rounding the width. Under board measure the width enters the surface measure carrying its fraction, and what rounds is the surface measure.
- Reading the export tally as a correction to board measure. The two are separate published methods, and the rules book gives board measure precedence where they disagree.
- Rounding everything the same way. Thickness rounds up to the next quarter and length rounds down to the whole foot on the same board.
- Summing a cut list before rounding the surface measure. Three boards of 6.5 by 8 by 2 give 24 board feet rounded per board and 26 rounded once at the end.
- Treating the two board foot figures as one being wrong. The trade tally comes from the rounded surface measure and the geometric volume from the dimensions, and both are correct answers to different questions.
- Assuming a quote is gross when the basis is not stated. A green tally arrives about seven percent light and a net tally does not, and an unstated quote could be either.
- Treating the scant allowances as short delivery. The Standard Kiln Dried Rule permits 1/16 inch on thin stock, 1/8 on 2 inch and thicker, and 1/4 inch on minimum widths.
- Expecting a grade from a calculator. Grade rests on the surface measure and on an inspection of the poor face, and this page reports the first and does not attempt the second.
- Comparing a per board foot price against an MBF price without converting. A thousand board feet is the wholesale unit and the two are not the same number.
Frequently Asked Questions
How do you calculate board feet?
How many board feet in a 2 by 4?
What does 4/4 mean in lumber?
Why is my 4/4 board only 13/16 thick?
What is surface measure?
Is the width rounded when you tally a board?
Why do two board foot figures differ?
What is the difference between net tally and green tally?
How much waste should I add for hardwood?
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Calculate
This selector governs every field, label, result and export here, and it overrides the site header switch. The nominal softwood sizes and the hardwood quarter designations do not convert, because they are trade designations rather than measurements.
The Lumber
Asked first because it decides which dimensions the trade bills on. Softwood is billed on the nominal size. Hardwood is billed on the rough thickness before surfacing. The fields below follow from this answer.
The Length and the Count
It selects the divisor. Twelve with the length in feet and 144 with the length in inches are the same equation, and there is no default that is right across the four units.
In the unit chosen above, and not in the unit system selector. A metric length is converted to feet before the board foot equation runs, because the board foot is an Imperial trade unit.
A whole number of boards of this size. One board is an answer and is entered as 1. The count multiplies into the order total and the linear feet.
The Cut List (optional)
In the same length unit as the first entry, because a cut list is one order in one convention.
A whole number of boards of this second size.
In the same length unit as the first entry.
A whole number of boards of this third size.
The Order
Trade guidance puts approximately 7 percent between the two. Not stated is an answer: the page then reports both readings and applies neither, because it cannot tell whether your figure is gross or net.
As a percentage, reported on its own line and never folded into the board foot figure. Published guidance gives 15 percent as a starting point for figured or character grade hardwood.
In your own currency. Any cost shown is arithmetic on this figure and nothing else.
Per thousand board feet, which is the unit lumber is wholesale priced in. Enter one price or the other: a per board foot price and a per MBF price are a thousand apart.