Board Foot & Lumber Cost Calculator
A 2x4 delivers 65.6% of the wood its name implies, and 4/4 hardwood is billed 33% above what it hands you.
A 2×4 is missing a third of the wood its name implies
Everyone knows a 2×4 is really 1½ by 3½. What gets missed is that the shortfall applies to both dimensions, and cross-section is a product — so it compounds. Nominal 2 × 4 is 8 square inches; actual 1.5 × 3.5 is 5.25. You receive 65.6%.
| Called | Actually | Nominal area | Real area | You get |
|---|---|---|---|---|
| 1x2 | 0.75 × 1.5″ | 2 | 1.13 | 56.3% |
| 1x3 | 0.75 × 2.5″ | 3 | 1.88 | 62.5% |
| 1x4 | 0.75 × 3.5″ | 4 | 2.63 | 65.6% |
| 1x6 | 0.75 × 5.5″ | 6 | 4.13 | 68.8% |
| 1x8 | 0.75 × 7.25″ | 8 | 5.44 | 68.0% |
| 1x10 | 0.75 × 9.25″ | 10 | 6.94 | 69.4% |
| 1x12 | 0.75 × 11.25″ | 12 | 8.44 | 70.3% |
| 2x2 | 1.5 × 1.5″ | 4 | 2.25 | 56.3% |
| 2x4 | 1.5 × 3.5″ | 8 | 5.25 | 65.6% |
| 2x6 | 1.5 × 5.5″ | 12 | 8.25 | 68.8% |
| 2x8 | 1.5 × 7.25″ | 16 | 10.88 | 68.0% |
| 2x10 | 1.5 × 9.25″ | 20 | 13.88 | 69.4% |
| 2x12 | 1.5 × 11.25″ | 24 | 16.88 | 70.3% |
| 4x4 | 3.5 × 3.5″ | 16 | 12.25 | 76.6% |
| 6x6 | 5.5 × 5.5″ | 36 | 30.25 | 84.0% |
And the fraction is not constant, which catches people substituting one size for another. A 1×2 delivers only 56.3% while a 6×6 delivers 84.0% — a fixed quarter inch off each face costs far more on a small section than a large one.
And hardwood is charged on the rough thickness
Hardwood sells by the board foot at its rough thickness. A 4/4 board is one inch rough and surfaces to three quarters, so an 8-inch by 8-foot board is billed at 5.33 board feet and hands you 4.00 of usable wood — you pay for 33.3% more than you receive. At $6 a board foot that is really $8 a board foot of wood you can work.
| Called | Rough | Surfaced 2 sides | Typical finished | You get |
|---|---|---|---|---|
| 4/4 | 1″ | 0.8125″ | 0.75″ | 75.0% |
| 5/4 | 1.25″ | 1.0625″ | 1″ | 80.0% |
| 6/4 | 1.5″ | 1.3125″ | 1.25″ | 83.3% |
| 8/4 | 2″ | 1.75″ | 1.75″ | 87.5% |
| 12/4 | 3″ | 2.75″ | 2.75″ | 91.7% |
| 16/4 | 4″ | 3.75″ | 3.75″ | 93.8% |
It is not a swindle — the planing is real work and the shavings are real wood — but it is a third, and it belongs in the estimate rather than in the surprise at the till. The gap shrinks as boards get thicker, which is one reason buying 8/4 and resawing can beat buying 4/4 twice.
Notes
- A board foot is 144 cubic inches — one inch by twelve by twelve. Thickness × width × length in inches, over 144. It is a volume, so a 1×12 and a 2×6 of the same length are the same board footage.
- Buy by the board foot, plan by the finished dimension. The two numbers are different and mixing them up is how a cut list runs short.
- Random widths and lengths are the norm for hardwood. You rarely choose the board's size, so add margin for the pieces that will not yield what you hoped.
- Softwood is sold by the piece at nominal size, hardwood by the board foot at rough thickness. Different trades, different conventions, and the same word "1 inch" means two different things.
How to use
- Pick the rough thickness — 4/4, 5/4 and so on.
- Enter the width and length in inches and how many boards.
- Read the board feet you are billed against the wood you receive.
- Add a price to see the real cost per usable board foot.
Frequently asked questions
How do you calculate board feet?
Thickness times width times length in inches, divided by 144 — because a board foot is 144 cubic inches, one inch by twelve by twelve. It is a volume, so a 1x12 and a 2x6 of the same length come to the same board footage.
Why is a 2x4 not 2 inches by 4 inches?
Because it is dressed after sawing, so it finishes at 1.5 by 3.5. The part that gets missed is that the shortfall applies to both dimensions and cross-section is a product — so you receive 65.6% of the wood the name implies. A third of it is not there.
Do all nominal sizes lose the same proportion?
No, and that catches people substituting sizes. A 1x2 delivers only 56.3% while a 6x6 delivers 84.0%, because a fixed quarter inch off each face costs far more on a small section than a large one.
What does 4/4 mean in lumber?
Four quarters of an inch — one inch, at rough thickness. It is how hardwood is sold and billed. After surfacing it is typically three quarters of an inch, so the board you work with is thinner than the board you paid for.
Am I paying for wood I do not get?
On surfaced hardwood, yes, and the figure is a third. A 4/4 board 8 inches by 8 feet is billed at 5.33 board feet and hands you 4.00 of usable wood — 33.3% more than you receive. At $6 a board foot that is really $8 of wood you can work.
Is that a swindle?
No. The planing is real work and the shavings are real wood, so the convention is defensible. It is simply large enough that it belongs in the estimate rather than in the surprise at the till.
Is it cheaper to buy thicker stock and resaw?
Often, because the proportional loss shrinks with thickness — 4/4 hands you 75% of its rough thickness while 8/4 hands you 87.5%. Whether that beats buying twice depends on your saw and how much you value the time, but the arithmetic favours the thicker board.
Why is softwood sold differently from hardwood?
Different trades and different conventions. Softwood is sold by the piece at a nominal size; hardwood by the board foot at rough thickness, usually in random widths and lengths. The same phrase "one inch" means two different things depending which yard you are standing in.
Does this send anything anywhere?
No. Everything is calculated in your browser and nothing is stored or uploaded.
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