Guide
Board Feet Explained: Lumber Math That Isn't Linear Feet
Published July 19, 2026
Board feet and linear feet diverge as soon as board thickness or width changes between pieces, which is exactly why lumber is priced by the board foot — it's a volume measure that accounts for how much actual wood is in a piece, not just how long it is.
The formula
Board feet = (thickness in inches x width in inches x length in feet) / 12. The 'divide by 12' exists because one board foot is technically defined as a piece 1 inch thick, 12 inches wide, and 1 foot long (144 cubic inches) — the formula scales any board's actual dimensions against that reference volume.
Worked example: same length, different sizes
A 1x6 board, 8 feet long: (1 x 6 x 8) / 12 = 4 board feet. A 2x6 board, also 8 feet long: (2 x 6 x 8) / 12 = 8 board feet — exactly double the 1x6, because it's twice as thick, even though both boards are the same 8 linear feet. A 2x10 board, 8 feet long: (2 x 10 x 8) / 12 = 13.3 board feet, nearly 3.5 times the 1x6 despite being the same linear length, since it's both thicker and wider.
This is why a linear-foot price comparison across different board sizes is misleading — a 2x10 costing twice as much per linear foot as a 1x6 isn't actually more expensive per unit of wood; it may well be a better value per board foot, since it contains far more material per foot of length.
Nominal vs. actual dimensions
A '2x4' isn't actually 2 inches by 4 inches once milled and dried — the actual dressed dimensions are closer to 1.5 x 3.5 inches, a standardized reduction from the rough-sawn nominal size. Board-foot calculations for pricing conventionally use the nominal size, not the actual dressed size, which is a detail worth knowing so the board-foot total you calculate matches how the lumberyard prices it, even though it doesn't match the exact wood volume you're physically getting.
Applying this to a project
For a project with mixed board sizes (like a furniture build or a raised garden bed frame with a mix of framing and cap-rail lumber), total board feet across the full cut list using the board feet calculator piece by piece, then buy stock lengths that minimize waste against your specific cut list rather than ordering the exact board-foot total in odd, mismatched lengths.
Board feet and lumber grading
Grade (a lumber quality classification based on knots, defects, and appearance) is priced per board foot on top of the base species price, so two boards with identical board-foot volume in the same species can cost meaningfully different amounts if one is a higher, clearer grade — this is worth factoring into a project budget separately from the raw board-foot quantity calculation, especially on a furniture or trim project where appearance grade matters more than on rough framing lumber.
Board feet in bulk lumber purchases
Buying lumber in bulk (a full unit or bundle rather than individual boards) is often quoted as a total board-foot price, which can be meaningfully cheaper per board foot than buying the same total volume as individual boards — this is worth checking against your project's actual board-foot need if you're buying enough material that a bulk unit purchase becomes practical, since the savings can be substantial on a larger project.
Board feet for round or irregularly-shaped stock
Live-edge slabs and other irregularly shaped stock don't fit the simple thickness-times-width-times-length formula cleanly, since width varies along the board's length — these are typically priced using an average or maximum width measurement specific to the piece, which is worth clarifying with the specific supplier since the calculation method can vary by yard for non-standard stock.
FAQ
Do all lumber types get priced by board foot?
Hardwoods (oak, walnut, maple, and similar) are almost always priced by the board foot, especially at a specialty lumberyard; construction softwood dimensional lumber (like standard 2x4s at a home center) is often priced per piece or per linear foot for common sizes, though the underlying board-foot volume is still the more accurate way to compare material cost across different board sizes.
Why does the formula divide by 12 instead of 144?
Because the formula already expresses length in feet rather than inches — dividing thickness (inches) x width (inches) x length (feet) by 12 correctly converts the mixed units to the standard board-foot reference volume; using length in inches would instead require dividing by 144.
Does board-foot pricing apply to sheet goods like plywood?
No — plywood and other sheet goods (OSB, MDF) are conventionally priced per sheet or per square foot of surface area, not by board foot, since they're a manufactured panel product rather than a milled solid-wood board, and the board-foot formula's thickness-times-width-times-length logic doesn't map cleanly onto a large flat sheet.
How much waste should I add when ordering board feet for a project?
A common allowance is 10-20% depending on the project's cut complexity and the lumber's grade — a simple, low-waste cut list from clear, high-grade stock needs less allowance than a project cutting around knots and defects in a lower grade, where more of the raw board foot total gets discarded to avoid those flaws.
Is it worth buying a full bulk unit of lumber if I only need a fraction of it for my current project?
It depends on whether you have realistic future use for the leftover material and appropriate dry storage for it — the per-board-foot savings on a bulk unit can be significant, but only if the surplus doesn't just sit unused and eventually degrade in storage.
Does moisture content affect board feet calculations?
Nominal board-foot volume is measured at the lumber's stated dimensions regardless of moisture content, but wood does shrink slightly as it dries from green to kiln-dried, so a board's actual measured dimensions (and therefore its true board-foot volume) can differ marginally from its nominal size depending on how thoroughly it's been dried.
How do I convert a linear-foot cut list into a board-foot purchase order?
Go piece by piece: multiply each cut's thickness by width by length (in feet), divide by 12, and sum the results across the whole list — this per-piece approach is more reliable than trying to shortcut with an average board size, since mixed thicknesses and widths in a real cut list don't average cleanly.
Why do some lumber suppliers quote a price per piece instead of per board foot for common sizes?
Standard construction sizes (like 2x4s and 2x6s in common lengths) are produced and sold in high enough volume that per-piece pricing is simpler for both the yard and the buyer, while less common sizes, hardwoods, or custom-milled stock are more often priced by board foot since piece-to-piece variation in size is more likely.