What Is a Board Foot? How to Measure and Buy Lumber
A board foot is a unit of volume used to sell lumber, especially hardwood. One board foot equals 144 cubic inches, which is a board 12 inches wide, 12 inches long, and 1 inch thick. Because it counts thickness along with width and length, it measures the actual amount of wood in a board, not just how long or wide it is.
What exactly is a board foot?
A board foot is 144 cubic inches of wood. Picture a plank one foot square and one inch thick: that is exactly one board foot. It is a volume measure, so a 1" board and a 2" board of the same width and length hold different amounts, and the board foot captures that difference. Length alone or area alone cannot.
This is why lumberyards use it. A linear foot tells you nothing about how wide or thick a board is, and a square foot ignores thickness entirely. The board foot rolls all three dimensions into one number, so a wide, thick plank and a narrow, thin one can be priced on the same honest scale.
How do you calculate board feet?
Multiply thickness, width, and length together, then divide by 144 when every measurement is in inches. If you have the length in feet, which is more common at the store, multiply thickness (inches) by width (inches) by length (feet) and divide by 12 instead. Both routes give the same answer.
- Measure in inches — record thickness and width in inches. A common board is 2" thick and 4" wide.
- Get the length — in inches for the ÷144 formula, or in feet for the ÷12 shortcut. Say the board is 8 feet long.
- Multiply the three numbers — 2 × 4 × 8 = 64.
- Divide — 64 ÷ 12 = 5.33 board feet for that single 2 × 4 × 8.
- Scale up — multiply by the number of identical boards, then by the price per board foot to get your total cost.
How many board feet are in common boards?
For dimensional lumber, board feet are figured on the labeled (nominal) size, so a 2×4 counts as a full 2 by 4. The table below lists board feet for standard 8-foot boards. Multiply by the actual length if yours differ, since the count scales directly with length.
| Board (nominal) | Length | Board feet |
|---|---|---|
| 1 × 4 | 8 ft | 2.67 |
| 1 × 6 | 8 ft | 4.00 |
| 1 × 8 | 8 ft | 5.33 |
| 1 × 12 | 8 ft | 8.00 |
| 2 × 4 | 8 ft | 5.33 |
| 2 × 6 | 8 ft | 8.00 |
| 2 × 8 | 8 ft | 10.67 |
| 2 × 10 | 8 ft | 13.33 |
| 4 × 4 | 8 ft | 10.67 |
Nominal vs actual size: which one do board feet use?
Board feet use the nominal size for dimensional and rough lumber, not the finished measurement. A "2×4" is labeled 2 by 4 but actually measures 1.5" × 3.5" after it is dried and planed. You still calculate and pay on the nominal 2 by 4, because that reflects the wood removed at the mill.
How is hardwood priced by the board foot?
Hardwood is sold at a dollar figure per board foot, so your cost is board feet times that rate. Compute the volume, then multiply. A 2" × 2" × 24" piece of walnut is (2 × 2 × 24) ÷ 144 = 0.67 BF; at $16.90 per board foot, that board runs about $11.27. Wider or thicker stock costs more because it holds more wood.
Hardwood thickness comes in a quarter system, where 4/4 means one inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is two inches. Each "quarter" is a quarter of an inch. Thicker 8/4 stock usually costs more per board foot than 4/4: it is harder to yield clear two-inch boards, it takes roughly two and a half times longer to dry, and it picks up more drying defects along the way.
Board foot vs linear foot vs square foot: what's the difference?
A linear foot measures only length. A square foot measures area, length times width. A board foot measures volume, length times width times thickness. Softwood construction lumber is often sold by the linear foot or by the piece, while hardwood and rough lumber are sold by the board foot because thickness varies so widely.
The distinction matters most when you compare prices. Two boards at the same price per linear foot can hold very different amounts of wood if one is thicker or wider. Converting everything to board feet puts them on equal footing, which is the whole reason the unit exists. For a full solid-wood project, the same volume idea underlies figuring bulk material.
Frequently asked questions
Is a board foot the same as a square foot?
No. A square foot measures area, which is length times width. A board foot measures volume and includes thickness, so it equals 144 cubic inches. Two boards can cover the same square footage yet contain different board feet if one is thicker.
How many board feet are in a 2×4×8?
A 2 × 4 that is 8 feet long holds 5.33 board feet. The math is (2 × 4 × 8) ÷ 12 = 5.33, using the nominal 2-inch by 4-inch size. If you priced it on the actual 1.5" × 3.5", you would undercount the wood.
Do I use nominal or actual lumber size for board feet?
Use the nominal size for dimensional and rough lumber. A 2×4 counts as a full 2 by 4 even though it dresses out to 1.5" × 3.5". Mill pricing is based on the as-sawn nominal size, which accounts for the material lost during planing.
What does 4/4 mean in hardwood?
It means one inch of nominal thickness. Hardwood uses a quarter system where the number over four counts quarter-inches: 4/4 is one inch, 6/4 is 1.5 inches, and 8/4 is two inches. Thicker stock generally costs more per board foot.
Why is lumber sold by the board foot instead of by length?
Because length alone ignores width and thickness. A board foot rolls all three dimensions into one number, so a wide thick plank and a narrow thin one can be priced fairly on the same scale. That is essential for hardwood, where board sizes vary a lot.
How do I convert board feet to cost?
Multiply your board feet by the price per board foot. If a project needs 40 board feet of oak quoted at $8 per board foot, that is 40 × $8 = $320 before tax. Figure the board feet first, then apply the rate.
Can a board foot be less than one?
Yes. Board feet are just a volume in units of 144 cubic inches, so small pieces come out as fractions. A 2" × 2" × 24" blank is 0.67 board feet, and a short thin offcut can be a tenth of a board foot or less.
Once the unit clicks, buying lumber gets simpler: measure thickness, width, and length, and let the volume drive the price. Enter your dimensions in the board foot calculator to get the board feet and cost for one board or a whole stack at once. For a solid-wood project measured by bulk volume rather than by the plank, the cubic yards calculator works the same dimensions the other way.