Board Foot vs Linear Foot vs Square Foot: What Each One Measures

Lumber math · Units · Updated 2026-09-13

Three units get used as if they were interchangeable at a lumber rack, and they measure three completely different things. A board foot is a unit of volume. A linear foot, also called a lineal foot or a running foot, is a unit of length. A square foot is a unit of area. Two boards that come to the same number of linear feet can differ by a factor of four in board feet, and the only thing that changed is the cross-section that the linear foot never counted.

This guide defines all three precisely, runs one physical board through each of them so you can see the same piece measured three ways, and lays out which unit a yard is likely to quote for which product. The full derivation of the board-foot formula lives in how to calculate board feet. Here the job is telling the three units apart, converting cleanly between them, and spotting the moment two suppliers are quoting the same wood in different units.

What each unit actually measures

A board foot is a volume: 144 cubic inches of wood. The reference piece is 1 in thick, 12 in wide and 12 in long. Any combination that multiplies out to 144 cubic inches is also one board foot, so a piece 2 in thick, 6 in wide and 12 in long is exactly one board foot as well. Because it is a volume, all three dimensions have to be in the number, and thickness is the one people drop. A cubic foot, for the record, is 1,728 cubic inches, which works out to 12 board feet.

A linear foot is one foot of length and nothing else. Lineal foot and running foot mean the same thing. Twelve linear feet of 1x2 pine and twelve linear feet of 8/4 by 12 in walnut are the same quantity in this unit, even though one is a stick you carry between two fingers and the other is a plank that takes two people. That is not a flaw in the unit, it is the point of it: when every piece coming off the rack has the same profile, length is the only variable left, so length is the only thing worth quoting.

A square foot is an area: one foot by one foot of face, 144 square inches. It ignores thickness the same way a linear foot ignores both thickness and width. A 4 ft by 8 ft sheet of plywood is 32 sq ft whether it is 1/4 in or 3/4 in thick, which is exactly why sheet goods are priced by thickness and grade as separate lines and not by the area alone.

• Lineal foot, linear foot and running foot are three names for one unit. A yard that says per foot on a trim rack means this one.
• Board measure, BM and FBM (foot board measure) all mean board feet. MBF means a thousand board feet and is how mill and truckload quantities are quoted.
• Surface measure, or SM, is the face area of a board in square feet, usually rounded to whole feet on a hardwood tally. It is a square-foot idea sitting on a board-foot ticket, which is its own small source of confusion.
• The cubic foot is not a normal quoting unit for North American lumber, even though a cubic foot is a perfectly good volume unit and holds 12 board feet.

One board, measured three ways

Take a rough 4/4 board, 6 in wide and 8 ft long, an ordinary piece of hardwood off a rack. It is 8 linear feet, because it is 8 ft long. Its face is 6 in wide, which is 0.5 ft, so the face is 0.5 ft x 8 ft, or 4 sq ft. Its volume is 1 x 6 x 8 divided by 12, which is 4 bf. Now put it back and pick up its 8/4 twin off the next rack: same 6 in width, same 8 ft length, twice the thickness.

The 4/4 row is where the trouble starts. At exactly 1 in thick the board-foot count and the square-foot count come out as the same number, 4 and 4, because multiplying an area by a thickness of one leaves it unchanged. Plenty of woodworkers meet lumber at 4/4, notice that the two numbers match, and carry that coincidence over to the 8/4 rack, where it is wrong by half. The real relationship is board feet = square feet of face x thickness in inches, and it only collapses into equality at 1 in.

Board feet per linear foot depends entirely on the cross-section

There is no fixed conversion between linear feet and board feet, and asking for one is the most common form of this question. The conversion factor is the cross-section itself: board feet per linear foot = thickness in inches x width in inches, divided by 12. A 1x4 runs 0.333 bf per linear foot. A 2x12 runs 2.000 bf per linear foot, six times the wood in the same foot of length. Both get quoted per linear foot at plenty of yards, and nothing in the quantity on either ticket hints at the difference.

Read both tables as rates, not totals: pick the row, then multiply by the length in feet. The hardwood table is built on rough thicknesses because hardwood is billed on the rough thickness even when the board arrives surfaced, which is worked through in what 4/4 lumber means. And because rough hardwood comes in random widths, you rarely get to use one row for a whole stack - you measure each board, which is the whole reason the board foot exists as a unit in the first place.

What the lumberyard sells by which unit

The unit a supplier quotes in is not arbitrary. It tracks how much the pieces vary. Where every piece is identical in section, length is enough, so trim goes by the linear foot. Where the pieces are a fixed rectangle of face, area is enough, so sheet goods and flooring go by the square foot. Where width and thickness both wander from board to board, only volume is fair to both sides, and that is hardwood and logs.

Two things fall out of that table. First, the same species can reach you under two different units on the same day: rough by the board foot at a hardwood dealer, surfaced by the linear foot at a home center. Second, the board foot is the only one of the three that survives a log, which is why log scale rules all report in board feet even though a standing tree has no faces to measure.

Every number keeps its unit. Board Foot Calculator₊ labels every result with the unit it belongs to - net board feet, waste, gross board feet - so a board-foot figure can never quietly pass for a square-foot or linear-foot figure once it lands in your notes. Tap any total and the working opens line by line with your own thickness, width and length echoed back. Coming soon on iPhone. Learn more about Board Foot Calculator₊.

Converting between the three

Every conversion below is one fact rearranged. Board feet = square feet of face x thickness in inches. Board feet = linear feet x thickness in inches x width in inches, divided by 12. Learn those two and you can move between any pair of units in your head at the rack, as long as you know the cross-section of what you are holding.

The quoting trap: two suppliers, one pile of wood

Here is the situation that costs money. You describe a job to two suppliers. One comes back with a quantity in board feet, the other with a quantity in linear feet, and the two numbers look nothing like each other even though the wood is identical. Nothing is wrong with either quote. They are simply counting different things, and until you put them in one unit there is no comparison to make.

Say the job needs twelve boards of rough 8/4 white oak, each 8 in wide and 10 ft long. Each board is 2 x 8 x 10 divided by 12, which is 13.333 bf, so the stack is 160 bf. The same stack is 120 linear feet, because twelve boards at 10 ft each is 120 ft of length. The same stack is 80 sq ft of face, because the face of one board is 8 in x 10 ft, or 6.667 sq ft, and twelve of those is 80 sq ft. One pile, three numbers, and the largest is double the smallest.

That last column is the part worth carrying around. A rate per linear foot has to be 1.333 times the rate per board foot to land on the same total for this stack, and a rate per square foot has to be 2 times it. Change the cross-section and both multipliers change with it, which is why a rule of thumb you worked out on one job will quietly mislead you on the next one.

1. Get the cross-section in writing: Thickness, width and length for what each supplier is actually shipping, and whether those are rough, surfaced, nominal or actual. Without the cross-section no conversion between these units is possible at all.
2. Pick one unit and move everything into it: For hardwood, make it the board foot. It is the only one of the three that tracks volume, so it is the only one that stays honest when widths and thicknesses vary across a stack.
3. Check what thickness the billing is on: Hardwood is billed on the rough thickness. A board quoted as 8/4 that arrives at 1-3/4 in surfaced is normal trade practice and not a short measure, but it does mean two quotes can describe the same finished thickness at different quarter figures.
4. Match the waste assumption: One quote may be net footage for the finished parts and the other gross with an allowance already folded in. Settle which before comparing, using the net and gross distinction in lumber waste factor.
5. Only then compare the rates: Once the quantities are in one unit, at one thickness basis, with one waste assumption, the per-unit rates finally mean something. How lumber is priced per board foot covers what else belongs in that comparison.

Which unit to think in

Think in board feet for anything you are going to cut up and rebuild into something else, because that is material you need a volume of. Think in linear feet for anything that stays the shape it came in, such as trim, banding and dowel, where you are buying a run and not a quantity of wood. Think in square feet for anything that covers a surface: sheet goods, flooring, veneer. Then write the unit down next to every number. Most of the expensive confusion in this category is not bad arithmetic, it is a correct number that lost its label somewhere between the rack and the checkout, and you can settle any of it with Board Foot Calculator or a phone and the two conversions above.

Frequently asked questions

Is a board foot the same as a linear foot?

No. A board foot is 144 cubic inches of wood, a measure of volume that uses thickness, width and length. A linear foot is one foot of length with the cross-section ignored entirely. The same 8 ft board is 8 linear feet whether it is 4/4 or 16/4, while its board footage changes by a factor of four across that range.

How many board feet are in a linear foot?

It depends completely on the cross-section, so there is no single answer. Multiply the thickness in inches by the width in inches and divide by 12 to get board feet per linear foot. A 1x6 comes to 0.500 bf per linear foot, an 8/4 by 6 in board comes to 1.000, and a 2x12 comes to 2.000.

How do I convert square feet to board feet?

Multiply the square feet of face by the thickness in inches, as long as every piece is the same thickness. So 32 sq ft of 4/4 stock is 32 bf, and the same 32 sq ft in 8/4 is 64 bf. If the pile mixes thicknesses, split it by thickness and convert each group separately.

Is a lineal foot the same as a linear foot?

Yes. Lineal foot, linear foot and running foot are three names for exactly the same unit of length, and you will hear all three in the same yard. None of them says anything about how thick or wide the piece is.

Why is hardwood sold by the board foot instead of by the foot?

Because rough hardwood comes in random widths and several thicknesses, so length alone would not describe what you are getting. A 10 ft board 5 in wide and a 10 ft board 11 in wide are the same number of linear feet and hold very different amounts of wood. The board foot is the unit that charges both sides fairly for the volume actually delivered.

Do I use nominal or actual size for board feet on a 2x4?

Use the nominal size when the yard is billing that way, which is the usual convention for dimensional softwood. Be aware of the gap: an 8 ft 2x4 counts as 5.333 bf nominal but its actual 1-1/2 by 3-1/2 in section holds 3.500 bf. Use the actual size when you are working out how much finished wood a project really has.

Is hardwood flooring sold by the board foot or the square foot?

By the square foot, normally in cartons that each cover a set area. Flooring is a covering, so area is what matters and thickness never enters the quantity. Measure the room in square feet, add a waste allowance for cuts and off-layout runs, then buy whole cartons.

Keep reading

• How to Calculate Board Feet: The Formula, Worked Examples and the Traps
• Board Foot Chart: Common Hardwood and Softwood Sizes
• Lumber Price Per Board Foot: How Hardwood Is Quoted and How to Compare Two Quotes