What a board foot actually is
A board foot is a unit of lumber volume equal to a piece of wood 1 inch thick, 12 inches wide and 12 inches long. That is 144 cubic inches. Hardwood yards, sawmills and woodworkers use it because boards come in odd widths and lengths, and pricing by volume keeps things fair. If you have ever bought oak or maple by the board, the tag at the yard was almost certainly quoted per board foot.
The formula
Board feet = thickness (inches) x width (inches) x length (feet) / 12. A single 2 x 6 that is 8 feet long, using the true 1 1/2 by 5 1/2 inch size, is 1.5 x 5.5 x 8 / 12 = 5.5 board feet. If the stock is thicker than 1 inch, simply multiply, as the formula already handles it. For several boards, multiply the one-board answer by the count.
If you work in metric, the calculator converts millimetres and metres for you. One board foot equals about 0.00236 cubic metres, so a cubic metre is roughly 424 board feet.
Nominal size versus actual size
This is where most Canadian orders go wrong. Softwood dimension lumber at a building supply store is sold by its nominal size, but a 2x4 does not measure 2 inches by 4 inches. After planing and drying, it is 1 1/2 by 3 1/2 inches. When you price framing lumber you usually pay per piece or per linear foot, so the actual size matters less. When you price rough or hardwood stock by the board foot, the thickness is quoted in quarters: 4/4 is about 1 inch, 8/4 is about 2 inches, and so on, measured before surfacing.
| Nominal | Actual (imperial) | Actual (metric) | BF per 8 ft |
|---|---|---|---|
| 2 x 4 | 1 1/2 x 3 1/2 | 38 x 89 mm | 3.5 |
| 2 x 6 | 1 1/2 x 5 1/2 | 38 x 140 mm | 5.5 |
| 2 x 8 | 1 1/2 x 7 1/4 | 38 x 184 mm | 7.25 |
| 2 x 10 | 1 1/2 x 9 1/4 | 38 x 235 mm | 9.25 |
| 2 x 12 | 1 1/2 x 11 1/4 | 38 x 286 mm | 11.25 |
| 4 x 4 | 3 1/2 x 3 1/2 | 89 x 89 mm | 8.17 |
If a mill or a yard quotes you by nominal size, a 2x4x8 is counted as 2 x 4 x 8 / 12 = 5.33 board feet even though the real piece holds 3.5. Always ask which method the price is based on.
How much lumber to buy
Add a waste factor. For straight cuts on clear boards, 10 percent is typical. For hardwood with knots, checks or color matching, plan on 15 to 20 percent. If you are cutting a tabletop from wide boards, think in terms of the widest usable board, not the total area. Bring your cut list, add the waste, round up the board feet, then compare with the lengths on the rack. Boards often come in random lengths, so you may end up buying a little more than the maths suggests.
Board foot cost examples
Prices change by species, grade and region, so use the price field in the calculator with a number from your own supplier. As a rough way to sanity check: if kiln dried red oak is quoted at a given price per board foot and you need 40 board feet, multiply and add your waste percentage. For a table with a 1 3/4 inch thick top using 8/4 stock, buy based on the rough thickness, since the mill charges for the 2 inches it started with.
Converting between units
To convert board feet to cubic feet, divide by 12. To convert board feet to square feet at a given thickness, divide by thickness in inches, so 24 BF of 1 inch stock covers 24 square feet. For linear feet, divide the board feet by the cross-section area in square inches over 12. For a 1x6, one linear foot is about 0.5 BF in nominal terms. If you need cubic volume for a shipping weight, check our lumber weight calculator or the cubic feet calculator.
Related planning tools
Framing a wall? The stud calculator tells you how many pieces you need before converting to board feet. Building the stairs for a deck? Use the stair calculator to size the stringers. For sheet goods, the plywood calculator works in sheets, not board feet.
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2 inch by 6 inch board that is 10 feet long has 10 board feet when you use nominal dimensions.
How many board feet are in a 2x4x8?
Using nominal size it is 5.33 board feet. Using the actual 1 1/2 by 3 1/2 inch size it is 3.5 board feet. Ask your supplier which they use.
How many board feet in a cubic metre?
About 424 board feet. One board foot is roughly 0.00236 cubic metres.
Is a board foot the same as a linear foot?
No. A linear foot measures length only. A board foot measures volume and depends on thickness, width and length together.
Do I use nominal or actual dimensions?
For rough or hardwood lumber priced by the board foot, use the thickness the supplier quotes, such as 4/4 or 8/4. For dressed softwood, nominal size is how most are priced, but the actual size is what you will build with.
How much extra lumber should I buy?
About 10 percent for clear straight stock and 15 to 20 percent for hardwood with defects or when matching grain.
Related calculators
Estimates only. See our disclaimer and how we calculate.