Board feet and linear feet answer different questions. Board feet measure volume. Linear feet measure length along a board, trim piece, rail, or timber. Confusing the two is one of the most expensive arithmetic errors in a material order, because it looks like a unit mismatch and behaves like a pricing error.
Two Units, Two Questions
A linear foot answers "how far does this piece run?" It ignores the cross-section entirely. Twelve linear feet of quarter-round moulding and twelve linear feet of 4×12 timber are the same linear quantity.
A board foot answers "how much wood is here?" It is a volume: 144 cubic inches. Because it folds thickness and width into the number, it can compare stock that is not the same size.
Neither unit is more correct. The right one is whichever matches how the material is sold and what decision you are making.
When Board Feet Help
Board feet are useful when thickness and width vary, especially with rough lumber, slabs, and stock sold by volume.
Hardwood dealers commonly price this way because their inventory arrives in random widths and lengths. A volume unit is the only fair basis when no two boards in the stack match.
- Rough-sawn hardwood sold in random widths.
- Live-edge slabs and other irregular stock.
- Mixed-size purchases where one price per unit has to cover several dimensions.
- Comparing quotes from suppliers whose stock is not dimensionally identical.
When Linear Feet Help
Linear feet are useful when the profile and cross-section are already fixed, such as trim, decking, framing members, and moulding.
If every piece has the same size, length-based pricing can be easier to use — and easier to check against a cut list, because your parts list is already written in lengths.
- Dimensional framing lumber sold by the piece or by the foot.
- Decking, cladding and fencing boards of a single profile.
- Moulding, trim and skirting where the profile is constant.
- Any takeoff where you already know the cross-section and only need to total run.
Conversion Formula
To convert linear feet to board feet you need thickness and width. The conversion only runs in one direction: with all three dimensions you can produce board feet, but board feet alone cannot recover a length.
That asymmetry is the whole point. Volume is a product of three numbers; knowing the product and one factor is not enough to find the others.
With the thickness and width known, the board foot to linear foot calculator runs the conversion both ways, on nominal or dressed size.
Board feet = (thickness in inches × width in inches × length in feet) / 12
Linear feet = board feet × 12 / (thickness in inches × width in inches)
Worked Example: Same Length, Different Volume
Ten linear feet of 2 inch by 6 inch rough stock is 10 board feet, because (2 × 6 × 10) / 12 = 10.
Ten linear feet of 1 inch by 6 inch stock is only 5 board feet: (1 × 6 × 10) / 12 = 5. The length is identical; halving the thickness halves the volume.
Now price them. At $5 per board foot the first piece costs $50 and the second costs $25. Quoted per linear foot, both might read "$X per foot" and hide that difference completely.
Comparing Two Quotes on the Same Basis
Suppose supplier A quotes $6.50 per board foot for 8/4 stock and supplier B quotes $9.75 per linear foot for the same nominal 8/4 × 6 inch material.
Convert B to a volume basis: one linear foot of 2 inch × 6 inch stock is (2 × 6 × 1) / 12 = 1 board foot, so B is effectively $9.75 per board foot — before checking whether either price is quoted on rough or dressed dimensions.
This is an illustrative comparison, not a market quote. The method matters more than the figures: put both prices on the same unit before judging which is cheaper.
Which Unit Belongs in a Cut List
A cut list is a list of parts, so it is written in lengths and cross-sections, not in board feet. Board feet enter only when you convert that parts list into a purchase.
Total the parts first, then apply a purchasing allowance. How Much Extra Lumber Should You Buy? covers why the cut-list total is never the purchase total.
For the volume arithmetic itself, see How to Calculate Board Feet.
Common Mistakes
Almost every error here is a unit that changed meaning between two steps without anyone noticing.
- Comparing a board-foot price with a linear-foot price without converting both to one basis.
- Using the nominal size name instead of the actual measured thickness and width.
- Assuming board feet can be recovered from length alone.
- Mixing inches and feet inside the formula — thickness and width in inches, length in feet.
- Treating a quarter designation such as 8/4 as a finished thickness rather than a rough one.
- Adding a waste allowance to the linear total and again to the converted volume.
Common questions
Can I convert linear feet to board feet?
Yes, but you need thickness and width. Length alone is not enough to calculate volume.
Which measurement should I use for a cut list?
Use the measurement that matches how the material is sold, then keep part dimensions in the cut list for layout.
What does a quarter measurement such as 4/4 or 8/4 mean?
It is a rough thickness expressed in quarters of an inch, so 4/4 is one inch and 8/4 is two inches. It describes the stock before surfacing, so the dressed board is usually thinner. Confirm with the supplier whether the price is tallied on the rough or the dressed dimension.
Why do two suppliers quote such different prices for the same species?
Often because the quotes are on different bases: board foot versus linear foot, rough versus dressed dimensions, or different grades. Convert both to one unit and confirm the dimensional basis before concluding one is cheaper.
Sources
- Valuing Standing Timber · Penn State Extension
Publishes the 144-cubic-inch board-foot definition and the inches-and-feet formula used for the conversion above.
- Wood Handbook, Chapter 6: Commercial Lumber, Round Timbers, and Ties · USDA Forest Service, Forest Products Laboratory
Documents hardwood thickness designations expressed in quarters and the distinction between rough and surfaced stock.