Board Foot Calculator
Length, width, thickness, and piece count in — board feet out, per piece and for the whole order, with a cost line at whatever price per board foot your supplier quotes. The formula is the industry's own: length (ft) × width (in) × thickness (in) ÷ 12.
Piece dimensions and count
Example: 10 pieces, 8 ft long at 3.5 × 1.5 in → 35 board feet.
Quantity estimates only — board-foot totals say nothing about structural adequacy, span capacity, code compliance, or engineering. Verify dimensions, grades, and local code with a professional.
Guide: Board feet, explained covers the unit itself — what a board foot measures, why a nominal 2×4 and a dressed 2×4 give different totals, and how a cut list becomes a priced order with waste and whole-board rounding. This page documents what the calculator does with the dimensions you type. The other concept guides are collected under Guides.
The board-foot formula, worked
One board foot is a 12 × 12 × 1 in slab of wood — 144 cubic inches. The definition anchor: an 8 ft board, 6 in wide and 1 in thick, is 8 × 6 × 1 ÷ 12 = 4 board feet exactly. The order example uses the dressed 2×4 section: 8 ft × 3.5 in × 1.5 in ÷ 12 = 3.5 board feet per piece, so 10 pieces total 35 board feet — at $4.50 per board foot, $157.50. Every figure on this page is computed by the same engine the form calls, at build time; if the arithmetic changed, the copy would change with it or the build would fail.
Nominal sizing matters when comparing quotes: under the sourced dressed sizes the site carries (PS 20-20, the American Softwood Lumber Standard published by NIST, Table 3), a surfaced softwood "2×4" has a minimum dry dressed size of 1.5 × 3.5 in, so its actual volume is 3.5 board feet per 8 ft stick, not the 5.333 the nominal numbers suggest. Hardwood dealers quote from their own (rough/quarters) sizing — match the convention your supplier uses. The guide tabulates the gap for every dressed size the site carries; here the point is only that the form applies no convention of its own.
What the calculator computes, step by step
Every result on this page comes out of the same short sequence, run on every keystroke by the engine that also produced the figures in this text.
- Read the length in feet. In imperial mode the feet box and the optional inches box are combined into decimal feet — feet plus inches ÷ 12, the same mixed-entry conversion the methodology page describes — so 9 ft 4 in becomes 9.3333 ft before anything is multiplied. In metric mode the metres box is divided by 0.3048, exact by the international definition of the foot.
- Read the cross-section in inches. Width and thickness are taken as decimal inches (1½ in is typed as 1.5). In metric mode the millimetre boxes are divided by 25.4, exact by the definition of the inch. The engine's canonical units never change: length in feet, section in inches, whichever system you type in.
- Board feet per piece. Length × width × thickness ÷ 12, carried at full floating-point precision. Nothing is rounded here.
- Multiply by the piece count. The pieces box takes a whole number of at least one and defaults to one when blank; the per-piece figure times the count is the order total, still unrounded, so a long order does not accumulate a rounding error per piece.
- Price only if you typed one. With a price per board foot in the box, the cost is the order total times that price. Leave the box blank and no cost line appears — the tool never supplies a price of its own.
- Volume equivalent. A board foot is one twelfth of a cubic foot (arithmetic on the definition: 1,728 cubic inches per cubic foot ÷ 144 per board foot = 12), so the total is divided by 12 for a cubic-feet readout; in metric mode that is multiplied by 0.028316846592 — 0.3048 cubed, exact — for cubic metres.
How to read the output
The result box carries up to four lines. The headline is the order total in board feet, shown to two decimals. The Per piece line shows the per-piece figure to three decimals and the count it was multiplied by, so a wrong count is visible at a glance. The Volume equivalent line is the same total as cubic feet, or cubic metres in metric mode. The Estimated lumber cost line appears only when a price was entered. Display rounding is the only rounding anywhere in the chain: the two-decimal total is a rounded view of an exact product, which is why the displayed per-piece figure times the count can differ from the headline in the last digit on a long order.
Copy result puts a one-line summary on the clipboard in the form "35 board feet (3.5 bd ft × 10), $157.50" for the worked order, ready to paste into a cut list or a message to a supplier. A value the form cannot parse is marked in its field; a value the engine rejects — zero, more than 1,000,000, a fractional piece count, a negative price — is explained in the result box instead.
Where this tool sits in the estimation pipeline
The estimators on this site share the five-stage pipeline documented on the methodology page: geometry, coverage, waste, package rounding, and user-priced cost. This calculator runs the first stage and the last and deliberately skips the three in between. Geometry is the whole of the board-foot formula: three dimensions and a count become a volume. There is no coverage stage because the board foot is itself the quoting unit this tool exists to produce — there is no package whose yield the volume must be divided by. There is no waste field because the tool totals pieces you have already counted; extra lumber is bought as whole boards, so a margin belongs on the piece count (the Deck Material Calculator applies the decking convention that way, and the worked deck example below shows the arithmetic). There is no package rounding because pieces are already whole and a board-foot total is never rounded up to anything. User-priced cost follows the same rule the methodology page states — a price you typed, nothing looked up — applied here to the unrounded board-foot total, because there is no package count to multiply.
Because no material coverage is involved, no constant on this page is a manufacturer figure. The figures the engine uses are definitions and arithmetic: 12 inches per foot (definition), 144 cubic inches per board foot and 12 board feet per cubic foot (arithmetic on that definition), 0.3048 m per foot and 25.4 mm per inch (exact by international definition), and 0.028316846592 m³ per cubic foot (0.3048 cubed). None is adjustable, because none is an estimate. The worked examples also use the site's sourced dry dressed lumber sizes — PS 20-20, Table 3, the constants the deck, fence, and post-hole tools default to — but this form does not apply them automatically: the cross-section is whatever you type. The one convention that appears below, the decking waste percentage, is a trade convention, labelled as such and adjustable on the tool that uses it.
Why each input matters
The formula is a plain product, so every input scales the answer in proportion: double the length, the width, the thickness, or the count and the total doubles. That makes the length box the one to check first on a surprising result, because it is the only field in feet, and the + inches box exists so that a tape reading such as 9 ft 4 in can be typed as it was read rather than converted by hand. Width and thickness multiply into the cross-section, and the cross-section is where the nominal-versus-dressed choice bites: the ten studs of the worked order come to 35 board feet at the dressed section and 53.33 at the nominal one, a gap of 18.33 board feet on a single small order. The pieces box is a count, not a length — the tool multiplies by it and refuses a fraction. The price box is optional and yours alone. The units toggle changes only how the boxes are read; the arithmetic behind them is identical in both systems.
Worked examples
Each example below is one run of the form, computed by the engine when this page was built. Prices, where shown, are the numbers typed into the price box for the example, not figures the site supplies.
The definition anchor
One piece, 8 ft long, 6 in wide, 1 in thick: 8 × 6 × 1 ÷ 12 = 4 board feet, and the volume line reads 0.333 cu ft. It is the case to type first when you want to be sure the boxes are in the units you think they are, because the check is the definition itself: the board's face is 8 ft × 0.5 ft = 4 sq ft, and a 1 in thick board covering one square foot is one board foot.
Ten studs, dressed and nominal, with a price
10 pieces at 8 ft, 3.5 × 1.5 in: 3.5 board feet each and 35 board feet for the order. With $4.50 in the price box the cost line reads $157.50. The same ten studs at their nominal 4 × 2 in name are 5.333 each and 53.33 in total — the figure to expect from a quote written on nominal size.
Fence posts with a feet-and-inches length
8 dressed 4×4 posts (3.5 × 3.5 in) at 9 ft 4 in: the length box holds 9, the inches box 4, and the engine works from 9.3333 ft — 9.528 board feet per post and 76.22 board feet for the eight. Typed as 9.4 in the feet box instead, the length would be 9 ft 4.8 in, not 9 ft 4 in; the misreadings section below puts a number on that slip.
Hardwood in quarters, priced
Rough hardwood is quoted on nominal quarters sizing, and 6/4 stock is six quarters of an inch: 1.5 in. 5 pieces at 10 ft × 7 in × 1.5 in are 8.75 board feet each and 43.75 board feet together; at a typed price of $7.25 per board foot the cost line is $317.19. This is the case the tool was built for — a quoting unit that a linear-foot count cannot produce.
Nominal 1×12 shelving
4 pieces at 10 ft, 12 in wide and 1 in thick nominal: 10 board feet per piece, 40 board feet in all. A nominal 12 in by 1 in section is 1 board foot per foot of length, which makes it a convenient mental check: for that one section, board feet and linear feet coincide.
Deck boards: a large priced order, then a margin
48 dressed 5/4×6 boards (5.5 × 1 in) at 16 ft: 7.333 board feet each, 352 board feet, and $1,091.20 at a typed $3.10 per board foot. To carry a margin, apply it to the count, not the total: 48 × (1 + 10 ÷ 100) = 52.8, rounded up to 53 boards, which run through the same form as 388.67 board feet and $1,204.87. The 10% is the decking trade convention the deck tool starts from — adjustable there, absent here by design.
Square timber and the volume line
2 dressed 6×6 timbers (5.5 × 5.5 in) at 12 ft: 30.25 board feet each, 60.5 board feet for the pair. The volume line reads 5.042 cu ft — the total ÷ 12 — and is the figure to use when a quantity of timber is being reckoned by volume rather than by the piece.
Metric entry
In metric mode, 20 pieces at 3 m × 140 mm × 45 mm are read as 9.8425 ft × 5.5118 in × 1.7717 in, then run through the identical formula: 8.009 board feet each and 160.19 board feet in total. The volume line reads 0.378 m³. As a check, the same twenty pieces measured directly in metres are 3 × 0.14 × 0.045 × 20 = 0.378 m³; the two routes agree because every conversion factor is exact.
Common misreadings
A decimal after the feet is not inches. The length box takes decimal feet, and the inches box takes inches; 8 ft 6 in belongs in the two boxes as 8 and 6, which the engine reads as 8.5 ft. Typed as 8.6 in the feet box alone it is 8 ft 7.2 in — a dressed 2×6 of that length is 5.913 board feet instead of 5.844. Small on one piece, and it compounds across a count.
Length in inches. The formula mixes feet and inches on purpose, so a length typed in the wrong unit swings the total by a factor of 12 — the same family of slip as the slab tools' inches-versus-feet thickness error. The ten-stud order with its 8 ft length typed as 96 comes to 420 board feet instead of 35. If a total looks about 12 times too large, look at the length box first.
Mixing conventions inside one piece. A nominal width with a dressed thickness — 4 in with 1.5 in — gives the ten studs 40 board feet, a figure that matches neither the dressed 35 nor the nominal 53.33. Use one convention for both section dimensions.
A board-foot total is not a piece count or a length. It is a volume. How many sticks it takes depends entirely on the stock length you cut from, and the pieces box is where the count goes — typing a total length there multiplies the order by that length. And the cost line is your typed price times the total, nothing more: no other charge is added, because the tool knows of none.
Where the model stops
The engine is pure arithmetic on three dimensions and a count. It does not know the species, grade, or moisture state of the wood; it deducts nothing for saw kerf, defects, or the offcut left when a piece is cut from a longer stock length; it does not choose stock lengths for a cut list; and it converts between nominal and dressed sizes only when you type the other figure. It carries no waste allowance and no price of its own, and it rounds nothing up. Different sections must be run separately and added — the Feet & Inches Calculator chains the lengths if those need adding too. A board-foot total is a material quantity and nothing more: it says nothing about structural adequacy or code compliance, and those are decisions for a licensed engineer, a code official, or a qualified contractor.
Frequently asked questions
What exactly is a board foot?
A volume unit for lumber: one foot of length by one foot of width by one inch of thickness — 144 cubic inches. The working formula is length in feet × width in inches × thickness in inches ÷ 12. An 8 ft board 6 in wide and 1 in thick is exactly 4 board feet.
Do I enter nominal or actual dimensions?
The tool computes whatever you give it. Hardwood dealers price rough lumber by board feet from nominal (quarters) sizing, while a surfaced softwood 2×4 actually measures about 1 1/2 × 3 1/2 in. If you are pricing against a dealer quote, use the sizing convention the dealer uses; if you are checking real volume, use actual dimensions.
How is this different from linear feet?
Linear feet measure length only and ignore the cross-section; board feet multiply the cross-section in. Trim and framing are commonly sold by the piece or linear foot, while hardwoods and custom milling are quoted per board foot — this tool converts your cut list into that quoting unit.
Can I total different board sizes in one order?
Run each size separately and add the totals — the Feet & Inches Calculator chains the additions if you are also totaling lengths. Each run multiplies one cross-section by one length and piece count, which mirrors how mills tally an order.
Where does the cost figure come from?
Total board feet times the price per board foot you enter — nothing is looked up or assumed. Lumber prices move constantly and vary by species, grade, and region, so the tool only prices from your number.
What is the "Volume equivalent" line under the result?
The same total expressed as a volume. A board foot is one twelfth of a cubic foot, so the tool divides the board-foot total by 12 to show cubic feet: the 60.5 board feet of two 12 ft dressed 6×6 timbers are 5.042 cu ft. In metric mode the same line reads in cubic metres, using the exact factor of 0.028316846592 m³ per cubic foot.
Why is there no waste field on this tool?
Because it totals a count of pieces you have already decided on, and extra lumber is bought as whole boards, not as a fraction of a board foot. Add the margin to the piece count and round up — 48 deck boards with the 10% decking convention become 52.8, so 53 boards — then run the rounded count through the tool. The Deck Material Calculator applies that convention for you, and the board-feet guide walks a cut list through the full pipeline.
What changes when I switch the form to metric?
Only the entry units. Length is read in metres and divided by 0.3048, width and thickness are read in millimetres and divided by 25.4, and the identical formula runs on the converted feet and inches — the result is still board feet, with the volume line in cubic metres. Twenty pieces of 3 m × 140 × 45 mm come to 160.19 board feet, 0.378 m³.
Related tools: the Flooring Calculator plans the boards that cover a floor, the Stair Calculator lays out the stringers this lumber becomes, and the Feet & Inches Calculator chains cut-list lengths exactly. The Construction Unit Converter covers any other unit move, and the Deck Material Calculator counts the joists and deck boards whose volume this tool prices.
Lumber figures are computed locally and never transmitted. Formula sources and the shared pipeline are documented on the methodology page.