How do you calculate board feet?

Nominal thickness in inches times nominal width in inches times length in feet, divided by 12. A 2x4x8 is 2 times 4 times 8 over 12, which is 5.33 board feet.

Is a board foot the actual volume of wood?

No. It uses the nominal size, so on a 2x4, which actually measures 1 1/2 by 3 1/2 in, about 34% of the billed volume is not physically present. One board foot is one twelfth of a cubic foot by definition, and the two would only agree if lumber were sold at its sawn size.

How much does a 2x4 weigh?

An 8 ft kiln dried 2x4 is about 9 lb at 30 lb per cubic foot. Green it can be 14, and freshly pressure treated closer to 17, because the treatment is waterborne. Weight is water weight and it moves more than anything else in the calculation.

A thousand board feet, from the Roman numeral M. It is the unit lumber is traded in: a price of $600 per MBF is 60 cents per board foot. Retail dimensional lumber is priced per piece instead, so converting back is the only honest way to compare sizes.

Is a 2x6 better value than a 2x4?

A 2x4x8 is 5.33 bf and a 2x6x8 is 8 bf, so a 2x6 is 1.5 times the wood. If it costs less than 1.5 times the price, it is cheaper per board foot. It also loses slightly less to dressing: 31% against 34%.

Do rough sawn boards measure their nominal size?

Close to it, yes. Rough stock has not been dressed, so a rough 2x4 is near a genuine two by four and its board feet and actual volume nearly agree. That is part of why it is priced differently.

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Board Foot Calculator

A board foot is nominal volume. A third of it is not there

A board foot is nominal thickness times nominal width times length, divided by twelve. It is not the volume of wood. A 2x4 measures an inch and a half by three and a half, so 34% of every board foot on the invoice is not there. That is the convention rather than a trick, and this shows both numbers at once.

Board feet and actual volume

Nominal thickness

Nominal width

Length

Pieces

no.

Density (typical, varies with moisture)

Your price per board foot (optional)

Board feet use the nominal size, as the trade bills them. Actual volume uses the dressed size, which is the wood you get.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

Nominal against actual, at the same scale

Worked example

One hundred 2x4s, 8 ft long, kiln dried.

Each. 2 × 4 × 8 / 12 = 5.33 board feet, on the nominal size.
Total. 533 bf, or 0.533 MBF, which is how lumber is traded.
Actual wood. 1.5 × 3.5 in over 800 linear feet is 29.17 cu ft.
The gap. A board foot is 1/12 cu ft, so 533 bf would be 44.4 cu ft if it were real. 34% of the billed volume is not there.
Weight. 29.17 cu ft at 30 lb/cu ft is 875 lb, or 8.8 lb a stick.

The 34% is not the same on every size. It is 34% on a 2x4, 31% on a 2x6 and 30% on a 2x12, because the half inch lost off the width matters less as the board gets wider. A 4x4 is the best of the common sizes at 23%.

The formula

Two volumes, and only one of them is wood:

bf = t_nom × w_nom × L / 12 cu ft = t_act × w_act × 12L / 1728

t, w nominal: 2 and 4 for a 2x4. What you are billed on
t, w actual: 1.5 and 3.5. What arrives
L: length in feet
MBF: a thousand board feet, the unit lumber is actually traded in

One board foot is one twelfth of a cubic foot by definition, so the two figures would agree if lumber were sold at its nominal size. It is not, and the gap is widest on the smallest sections.

Why a 2x4 is not two by four

Lumber is sawn at the nominal size and then dried and dressed, and both take material off. What arrives has been planed on four sides to a standard finished dimension, and those dimensions are set by the American Softwood Lumber Standard PS 20.

The convention that survived is that the board is still named and billed at the size it was sawn at. That is why board feet use the nominal dimensions: the unit is a measure of the log's output, not of the timber in your hand.

The gap is not constant. A 2x4 loses 34% of its nominal area, a 2x6 loses 31% and a 2x12 loses 30%, because the half inch taken off the width is a smaller share of a wider board. A 4x4 does best of the common sizes at 23%. Anyone comparing prices per board foot across sizes is comparing slightly different things.

Rough sawn lumber is the exception worth knowing. It has not been dressed, so a rough 2x4 is close to a genuine two by four, and its board feet and its actual volume nearly agree. That is part of why rough stock is priced the way it is.

Weight, and why it moves so much

Wood weight is water weight. Kiln dried softwood at 19% moisture content runs roughly 28 to 32 lb per cubic foot. The same species green off the saw can be 45 to 50, and freshly pressure treated lumber can exceed 60 because the treatment is carried in water.

The practical consequences are load and shrinkage. A pallet of treated 2x6 delivered wet is substantially heavier than the same pallet six months later, and every one of those boards will shrink across its width as it dries. That is why treated deck boards are usually gapped tighter than dry ones: they are going to open up on their own.

If weight actually matters, for a lift or a load calculation, weigh a piece. The density options here are typical values and the spread between them is larger than any error you are likely to make elsewhere in the calculation.

MBF, and why lumber is quoted that way

Lumber is traded in thousands of board feet, written MBF, from the Roman numeral. A price of $600 per MBF is 60 cents a board foot, and futures, mill quotes and market reports all use MBF.

Retail is different: dimensional lumber is usually priced per piece, and converting back to a board foot price is the only way to compare a 2x4 against a 2x6 honestly.

A 2x4x8 is 5.33 bf. A 2x6x8 is 8 bf. If the 2x6 is less than 1.5 times the price of the 2x4, it is cheaper wood.

Where board feet are the wrong unit

Sheet goods are sold by the sheet and quoted per square foot, not per board foot. The sheathing calculator handles those.

Framing is easier to order in pieces than in board feet, because you are buying specific lengths. The wall framing calculator gives both, so you can order in pieces and check the invoice in board feet.

Hardwood is where board feet genuinely earn their place, because it is sold in random widths and lengths and quoted in quarters: 4/4 is one inch nominal, 8/4 is two. There the board foot is the only sensible unit.

Frequently asked questions

How do you calculate board feet?: Nominal thickness in inches times nominal width in inches times length in feet, divided by 12. A 2x4x8 is 2 times 4 times 8 over 12, which is 5.33 board feet.
Is a board foot the actual volume of wood?: No. It uses the nominal size, so on a 2x4, which actually measures 1 1/2 by 3 1/2 in, about 34% of the billed volume is not physically present. One board foot is one twelfth of a cubic foot by definition, and the two would only agree if lumber were sold at its sawn size.
Why is a 2x4 actually 1.5 by 3.5 inches?: It is sawn at two by four and then dried and dressed on four sides, which takes material off. The finished dimensions are set by the American Softwood Lumber Standard PS 20, and the convention is that the board keeps the name and the billing of the size it was sawn at.
How much does a 2x4 weigh?: An 8 ft kiln dried 2x4 is about 9 lb at 30 lb per cubic foot. Green it can be 14, and freshly pressure treated closer to 17, because the treatment is waterborne. Weight is water weight and it moves more than anything else in the calculation.
What is MBF?: A thousand board feet, from the Roman numeral M. It is the unit lumber is traded in: a price of $600 per MBF is 60 cents per board foot. Retail dimensional lumber is priced per piece instead, so converting back is the only honest way to compare sizes.
Is a 2x6 better value than a 2x4?: A 2x4x8 is 5.33 bf and a 2x6x8 is 8 bf, so a 2x6 is 1.5 times the wood. If it costs less than 1.5 times the price, it is cheaper per board foot. It also loses slightly less to dressing: 31% against 34%.
Do rough sawn boards measure their nominal size?: Close to it, yes. Rough stock has not been dressed, so a rough 2x4 is near a genuine two by four and its board feet and actual volume nearly agree. That is part of why it is priced differently.

Check these numbers yourself

PS 20, American Softwood Lumber StandardAmerican Lumber Standard Committee. PS 20 in full, including the dressed size tables that set why a 2x4 is 1 1/2 by 3 1/2 in. Free PDF.
American Lumber Standard CommitteeThe committee that administers PS 20 and accredits the grading agencies whose stamps appear on lumber.
USDA Wood HandbookForest Products Laboratory. Specific gravity and moisture relations, which is where wood density figures come from and why they vary so much.

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

Board feet are a billing unit, not a volume. They use nominal dimensions and overstate the wood present by 23 to 34% depending on the size. Density figures are typical values only: moisture content moves weight by half again, so weigh a piece if the weight matters.