If you have ever bought hardwood or ordered rough lumber, you have seen prices quoted per board foot rather than per piece. It catches a lot of people off guard, because a board foot is a measure of volume, not length. Once you understand it, comparing lumber prices becomes easy.
The definition
A board foot is a unit of volume equal to a piece of wood 12 inches wide, 12 inches long, and 1 inch thick. That works out to 144 cubic inches. Any board with that same volume is one board foot, whether it is a wide thin plank or a narrow thick one.
Because it measures volume, a board foot tells you how much actual wood you are buying, which is why lumber yards use it to price boards of different widths and thicknesses fairly.
The formula
To calculate board feet, use the thickness and width in inches and the length in feet:
Board feet = (thickness in × width in × length ft) ÷ 12
You divide by 12 because there are 12 inches in the foot of length. If you prefer to work entirely in inches, use length in inches and divide by 144 instead.
Worked examples
A 2 inch by 8 inch board that is 10 feet long: 2 times 8 times 10, divided by 12, is about 13.3 board feet.
A 1 inch by 6 inch board that is 8 feet long: 1 times 6 times 8, divided by 12, is 4 board feet.
If you are buying several of the same board, calculate one and multiply by the quantity. Ten of those 1 by 6 boards would be 40 board feet.
Nominal size versus actual size
Here is the part that trips people up. A “2 by 4” is not actually 2 inches by 4 inches. That is the nominal size, the rough dimension before the board is dried and planed smooth. The actual size of a finished 2 by 4 is about 1.5 by 3.5 inches.
For construction lumber priced by the piece, this does not matter for your board foot math, because dimensional lumber is usually sold and priced per piece, not per board foot. But for hardwood and rough-sawn lumber, which is where board feet really come into play, you often measure the actual dimensions. Rough hardwood is frequently sold in quarter-inch thickness steps, written as 4/4 (one inch), 5/4, 6/4, and 8/4. A 4/4 board is a nominal one inch thick.
When in doubt, ask the yard whether they price on nominal or actual dimensions, since it changes the total.
Why it matters for a project
Board feet let you do two things quickly:
- Compare prices. A wide plank and a narrow one can be priced per board foot so you know which is truly cheaper per unit of wood.
- Estimate a whole order. Add up the board feet for every piece on your cut list, then multiply by the price per board foot for a total material cost before you leave home.
Let the calculator do the arithmetic
Our board foot calculator takes the thickness, width, length, and quantity and returns the total board feet, so you can price an order in seconds. For framing projects measured by the piece, the lumber calculator and the framing lumber calculator handle studs, plates, and joists directly.
Frequently Asked Questions
Is a board foot the same as a linear foot?
No. A linear foot is just length, with no consideration for width or thickness. A board foot is a unit of volume equal to 12 by 12 by 1 inch. A 1 by 12 board that is 1 foot long is exactly one board foot. A 1 by 6 board of the same length is half a board foot, even though both are one linear foot long.
How many board feet are in a standard 2x4x8?
Using actual dimensions (1.5 by 3.5 by 8 feet): 1.5 times 3.5 times 8 divided by 12 equals about 3.5 board feet. Using nominal dimensions (2 by 4 by 8), the calculation gives about 5.3 board feet. Hardwood dealers typically use nominal or rough dimensions for pricing. Check with your supplier which they use.
Why is hardwood priced by the board foot instead of by the piece?
Because hardwood boards vary widely in width and thickness, unlike dimensional softwood framing lumber which comes in standard sizes. A price per board foot makes it possible to compare boards of different dimensions fairly. Two boards with the same board footage contain the same volume of wood regardless of their shape.
What does nominal lumber size mean?
Nominal size is the size of the board when it was first sawn from the log, before kiln drying and planing. Drying shrinks the wood, and planing removes more material to make it smooth and flat. A 2x4 was once 2 inches by 4 inches rough-sawn, but after processing it measures 1.5 by 3.5 inches. Nominal sizes are used in framing calculations and lumber ordering; actual sizes matter for joinery and finish work.
How do I convert board feet to linear feet?
Divide the board feet by the width in inches times the thickness in inches, then multiply by 12. For a 1 by 6 board: linear feet equals (board feet / (1 × 6)) × 12. So 24 board feet of 1 by 6 equals 24 / 6 × 12 = 48 linear feet. This conversion is useful when you know the total board footage you need but want to know how many feet of a specific board to buy.
Do hardwood dealers sell by actual or nominal dimensions?
Most hardwood dealers use actual rough-sawn dimensions for pricing, not dressed dimensions. A board listed as 1 inch thick is likely 1 inch rough, which finishes to about 13/16 inch after surfacing. Ask the dealer whether prices are quoted for rough or surfaced material, and whether thickness is before or after surfacing, to avoid surprises when the board arrives.