Walk into a lumber yard and you'll be quoted in two different units depending on which aisle you're standing in. They aren't interchangeable, and the difference isn't academic — it's the difference between a quote you can trust and one that's wrong by a factor of several.
Linear foot: just length
A linear foot is one foot of length, full stop. The width and thickness don't enter into it.
An 8-foot 2×4 is 8 linear feet. So is an 8-foot 2×12 — even though it holds three times the wood. That's why linear-foot pricing only makes sense when everyone already knows the dimensions, which is exactly the case with standard construction lumber.
Board foot: volume
A board foot is 144 cubic inches of wood. Picture a piece 12 inches square and 1 inch thick — that's one board foot.
Or if your length is already in feet: (thickness in × width in × length ft) ÷ 12
An 8-foot 2×6: (2 × 6 × 96) ÷ 144 = 8 board feet. Our board foot calculator runs this for any dimensions, and the lumber calculator handles the cost side.
Why a 2×4 isn't 2 by 4
Here's the part that catches everyone, and it's the source of most board-foot mistakes.
A 2×4 actually measures 1.5 × 3.5 inches. The "2×4" is the nominal size — what it measured when rough-sawn, before it was dried and planed smooth. The name stuck; the wood shrank.
| Nominal | Actual |
|---|---|
| 1×4 | 0.75 × 3.5 in |
| 2×4 | 1.5 × 3.5 in |
| 2×6 | 1.5 × 5.5 in |
| 2×8 | 1.5 × 7.25 in |
| 2×10 | 1.5 × 9.25 in |
| 4×4 | 3.5 × 3.5 in |
Hardwood plays by different rules
Hardwood is sold by the board foot, and thickness is quoted in quarters of an inch:
| Quarter | Rough thickness | After planing |
|---|---|---|
| 4/4 ("four-quarter") | 1 in | ~0.75 in |
| 5/4 | 1.25 in | ~1 in |
| 8/4 | 2 in | ~1.75 in |
Hardwood also comes in random widths and lengths — you buy a quantity of wood, not a list of pieces. That's precisely why board feet exist: it's the only fair way to price boards that aren't uniform.
And note you're usually charged for the rough board footage even when you buy it surfaced. You pay for the wood before it was planed away. That's normal, and it's worth knowing before you feel cheated at the till.
Which unit applies where
| Buying | Sold by |
|---|---|
| Framing lumber (2×4, 2×6) | Piece or linear foot |
| Decking boards | Piece or linear foot |
| Hardwood (oak, walnut, maple) | Board foot |
| Rough-sawn lumber | Board foot |
| Plywood / sheet goods | Per sheet |
Buying tips
Add 10–15% waste. Cuts, defects, and mistakes. Add more for anything with angles or patterns.
Sight down every board. Warp doesn't show flat in a stack. Look along the edge — crooked lumber is why the pile at the back of the rack is still there.
Compare like with like. Converting a board-foot price to a per-piece price before comparing suppliers is the only way to know who's actually cheaper.
For a full project, our lumber calculator handles board feet and cost together, and the decking calculator converts a deck size straight into boards and joists.
Try the free calculator
Skip the manual math — get instant numbers for your own project:
Frequently Asked Questions
What is the difference between a board foot and a linear foot?
A linear foot measures length only, while a board foot measures volume — 144 cubic inches, equal to a piece 12 by 12 by 1 inch. Hardwood is sold by board foot, framing lumber by linear foot or piece.
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in inches, then divide by 144. If your length is in feet, divide by 12 instead.
Why is a 2x4 not actually 2 by 4 inches?
The 2x4 is the nominal size from when the board was rough-sawn. After drying and planing it measures about 1.5 by 3.5 inches, but the original name stuck.
Is hardwood sold by board foot or linear foot?
Board foot, because hardwood comes in random widths and lengths. Thickness is quoted in quarters of an inch, so 4/4 means one inch rough.