An 8-foot 2x4 is 5.33 board feet. A 10-footer is 6.67, a 12-footer is 8, and a 16-footer is 10.67.
The formula behind all of those is thickness times width times length in feet, divided by 12, using the nominal 2x4 size and not the 1.5 by 3.5 it actually measures.
The 2x4, worked through
A board foot is a volume: one square foot of wood an inch thick, or 144 cubic inches. To get board feet from a piece of lumber you multiply thickness in inches by width in inches by length in feet, then divide by 12.
2 in × 4 in × 8 ft ÷ 12 = 5.33 board feet
Change the length and only the last number moves. A 2x4 gains 0.667 board feet for every extra foot, so the common yard lengths land at 5.33, 6.67, 8, and 10.67.
Common dimensional lumber
All figures use nominal sizes, which is how lumber is priced.
| Size | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 2x4 | 5.33 | 6.67 | 8.00 | 10.67 |
| 2x6 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2x8 | 10.67 | 13.33 | 16.00 | 21.33 |
| 2x10 | 13.33 | 16.67 | 20.00 | 26.67 |
| 2x12 | 16.00 | 20.00 | 24.00 | 32.00 |
| 1x4 | 2.67 | 3.33 | 4.00 | 5.33 |
| 1x6 | 4.00 | 5.00 | 6.00 | 8.00 |
| 1x8 | 5.33 | 6.67 | 8.00 | 10.67 |
| 1x12 | 8.00 | 10.00 | 12.00 | 16.00 |
| 4x4 | 10.67 | 13.33 | 16.00 | 21.33 |
| 6x6 | 24.00 | 30.00 | 36.00 | 48.00 |
A few of those repeat, and the repeats are useful to notice. A 2x8 and a 4x4 hold the same wood, and so do a 2x6 and a 1x12. Board feet only care about volume, so different shapes with the same cross-section come out identical.
Why the nominal size is the one you use
Put a tape on a 2x4 and you get 1.5 by 3.5 inches. The 2x4 name describes the rough-sawn board before it was planed smooth and dried, and the industry never renamed it. That gap matters here because board feet, and the price per board foot, are figured on the nominal size.
Run the same 8-footer on its actual dimensions and you get 3.5 board feet instead of 5.33, about a third less. Do that across a whole order and you will be a third short at the yard, with the wrong idea of what it should cost. Nominal in, nominal out.
When board feet matter, and when they do not
Most people buying 2x4s at a box store never see a board-foot price. Dimensional softwood is usually sold by the piece, and you pay for a 2x4x8 whatever that sticker says. Board feet come into it when you are buying hardwood, buying in bulk from a lumber yard, or comparing prices across different sizes, where a per-piece price tells you nothing.
That last case is where the unit earns its keep. Two yards quoting different sizes at different piece prices are impossible to compare until you put both on a per-board-foot basis. Then it is one number against another.
Run any size and quantity through the Lumber Calculator, or see the general method in how to calculate board feet. For where softwood prices sit this month, the Lumber Price Index tracks the federal figure.
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Open the Lumber CalculatorFrequently asked questions
5.33 board feet. The math is 2 inches thick, times 4 inches wide, times 8 feet long, divided by 12. Every 2x4 works the same way, so a 10-footer is 6.67 and a 12-footer is 8. Use the nominal 2x4 for this, not the 1.5 by 3.5 it actually measures.
6.67 board feet, from 2 x 4 x 10 divided by 12. Two more feet of length adds 1.33 board feet, which is the same step you get going from any 2x4 length to the next one up.
About 19 eight-footers, since each is 5.33 board feet and 100 divided by 5.33 is 18.75. In 12-footers it is exactly 12.5, so 13 boards. The longer the stick, the fewer you need, so yards quote per board foot instead of per piece whenever lengths are mixed.
No. A 2x4 measures about 1.5 by 3.5 inches once it has been planed and dried. The 2x4 name is the rough-sawn size before finishing. Board feet, pricing, and every table you will find all run off the nominal 2x4, so that is the number to use even though it is not what your tape shows.
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