How to calculate board feet
A board foot is a unit of volume: a piece of wood 1 in. thick, 12 in. wide and 12 in. long, or 144 cubic inches. Hardwood lumber yards and sawmills price by the board foot because rough boards come in random widths and lengths, so counting pieces doesn't work. To find board feet, multiply the three dimensions and divide by the size of one board foot.
Board feet = thickness (in) × width (in) × length (in) ÷ 144
Total = board feet per board × number of boards
Twelve board feet make one cubic foot, so you can convert in either direction: cubic feet = board feet ÷ 12. One cubic meter is about 424 board feet.
Worked example: ten 4/4 boards, 6 in. wide and 8 ft long
- Thickness: 4/4 means four quarters, or 1 in.
- One board: 1 × 6 × 8 ÷ 12 = 4 board feet.
- Ten boards: 4 × 10 = 40 board feet.
- Add 20% for defects and cutoffs: 40 × 1.20 = 48 board feet to buy.
- Volume: 40 ÷ 12 = 3.33 cu ft.
If your yard charged a hypothetical $8 per board foot, those 48 board feet would cost 48 × 8 = $384. Thicker stock adds up fast: a single 8/4 board 7 in. wide and 10 ft long is 2 × 7 × 10 ÷ 12 = 11.67 board feet.
Quarter thickness: what 4/4, 5/4 and 8/4 mean
Hardwood thickness is stated in quarters of an inch, measured when the board is rough sawn. A board sold as 4/4 ("four quarter") started at about 1 in. thick. After it is surfaced on both faces (S2S), it is thinner, but you still pay for the rough thickness. The surfaced sizes below are common standards; individual mills vary a little.
| Quarter size | Rough thickness | Typical surfaced (S2S) | Board feet per linear ft, 6 in. wide | Board feet in a 6 in. × 8 ft board |
|---|---|---|---|---|
| 4/4 | 1 in. | about 13/16 in. | 0.50 | 4 |
| 5/4 | 1-1/4 in. | about 1-1/16 in. | 0.625 | 5 |
| 6/4 | 1-1/2 in. | about 1-5/16 in. | 0.75 | 6 |
| 8/4 | 2 in. | about 1-3/4 in. | 1.00 | 8 |
| 10/4 | 2-1/2 in. | about 2-1/4 in. | 1.25 | 10 |
| 12/4 | 3 in. | about 2-3/4 in. | 1.50 | 12 |
| 16/4 | 4 in. | about 3-3/4 in. | 2.00 | 16 |
If a project calls for a finished thickness of 3/4 in., buy 4/4. For a finished 1 in. tabletop, buy 5/4. Plan your cut list in finished sizes, then pick the quarter size that leaves enough to flatten and plane the board.
Board feet vs. linear feet
A linear foot measures length only. A board foot measures volume. Home centers sell dimensional softwood lumber (2×4s, 2×6s, deck boards) by the piece or by the linear foot, so you rarely need board feet there. Hardwood dealers, sawmills and many lumber yards price by the board foot, and contractors' lumber packages are often quoted per thousand board feet (MBF).
Board feet for dimensional lumber are traditionally figured from nominal sizes, so a 2×4 counts as 2 × 4 in., not its actual 1-1/2 × 3-1/2 in.
| Nominal size | Board feet per linear ft | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|---|
| 1×4 | 0.333 | 2.67 | 3.33 | 4.00 | 5.33 |
| 1×6 | 0.50 | 4.00 | 5.00 | 6.00 | 8.00 |
| 1×8 | 0.667 | 5.33 | 6.67 | 8.00 | 10.67 |
| 1×12 | 1.00 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2×4 | 0.667 | 5.33 | 6.67 | 8.00 | 10.67 |
| 2×6 | 1.00 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2×8 | 1.333 | 10.67 | 13.33 | 16.00 | 21.33 |
| 2×10 | 1.667 | 13.33 | 16.67 | 20.00 | 26.67 |
| 2×12 | 2.00 | 16.00 | 20.00 | 24.00 | 32.00 |
| 4×4 | 1.333 | 10.67 | 13.33 | 16.00 | 21.33 |
| 6×6 | 3.00 | 24.00 | 30.00 | 36.00 | 48.00 |
How much waste to allow
Rough hardwood is graded by how much clear wood you can cut from a board, not by how perfect the whole board is. Knots, end checks, wane, sapwood you don't want and snipe from the planer all end up as scrap. Allowances of about 15–30% are typical for furniture projects in rough lumber; use the high end for lower grades, figured wood you want to match, or cut lists with many short or narrow parts. Clear, surfaced boards bought for simple shelving or trim can often get by with 10% or less.
Tips for buying lumber by the board foot
- Tally as you pick. Rough boards vary in width, so measure each one and add them up, or bring the yard's tally sheet. The calculator's number of boards field works best when the boards are similar in size.
- Ask how the yard measures. Some dealers round each board to the nearest board foot or count thin stock as 1 in. thick. Prices can also differ for surfaced versus rough stock.
- Buy a little long. Ends are often checked, so plan to trim a few inches from each end of a rough board.
- Building outdoors? Use the deck calculator for deck boards and joists and the fence calculator for posts, rails and pickets, then estimate finish with the deck stain calculator.
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. If all three are in inches, divide by 144 instead. A 1 in. × 6 in. × 8 ft board is 1 × 6 × 8 ÷ 12 = 4 board feet.
How many board feet are in a 2×4×8?
About 5.33 board feet, figured from the nominal size: 2 × 4 × 8 ÷ 12 = 5.33. A 2×6×8 is 8 board feet and a 2×4×10 is 6.67.
What does 4/4 mean in lumber?
It means four quarters of an inch, or 1 in. thick when rough sawn. 5/4 is 1-1/4 in., 8/4 is 2 in. and so on. Surfaced 4/4 hardwood usually measures about 13/16 in. thick, but it is still priced as 4/4.
What is the difference between a board foot and a linear foot?
A linear foot is 12 in. of length, regardless of size. A board foot is a volume of 144 cubic inches (1 × 12 × 12 in.). A 1×12 board has 1 board foot per linear foot; a 1×6 has half a board foot per linear foot.
How many board feet are in a cubic foot?
Twelve. A board foot is 144 cubic inches and a cubic foot is 1,728 cubic inches, so 1,728 ÷ 144 = 12.
How much extra hardwood should I buy?
Typically 15–30% more than your cut list for rough hardwood, to cover knots, checks, defects and planing. Clear, surfaced boards for simple projects may need only about 10% extra.
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