A board foot is a piece of wood 12 in long, 12 in wide and 1 in thick, or the same volume in any shape: 144 cubic inches. To find board feet, multiply thickness × width, both in inches, by the length in feet, and divide by 12. A 2x4 8 ft long is 5.33 board feet.
The formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12. If you measure the length in inches too, divide by 144 instead. These lines follow the boards in the calculator above:
Nominal sizes, actual sizes and thin boards
The USDA’s Wood Handbook sets out how lumber is counted: for lumber 1 in or more thick, board feet are figured on the nominal thickness and width, the size it is sold as, and the actual length. Lumber with a nominal thickness under 1 in is counted as 1 in.
So a 2x4, which the American Softwood Lumber Standard sizes at 1½ × 3½ in when dry (Wood Handbook, Table 6–6), still counts as 2 × 4 in. A 1/2 in board is counted as if it were 1 in thick, and the calculator does the same.
Hardwood in quarters
Hardwood is sold rough, by thickness in quarters of an inch: 4/4 (“four quarter”) is 1 in, 8/4 is 2 in. It usually comes in random widths, and the Wood Handbook gives standard lengths of 4 to 16 ft in 1 ft steps. Board feet are figured on the rough thickness, so planed boards come out thinner than the number you paid for:
| Thickness | Rough | Planed both faces (S2S) | Board feet per foot of 6 in board |
|---|---|---|---|
| 4/4 | 1 in | 13/16 in | 0.5 |
| 5/4 | 1-1/4 in | 1-1/16 in | 0.625 |
| 6/4 | 1-1/2 in | 1-5/16 in | 0.75 |
| 8/4 | 2 in | 1-3/4 in | 1 |
| 10/4 | 2-1/2 in | 2-1/4 in | 1.25 |
| 12/4 | 3 in | 2-3/4 in | 1.5 |
| 16/4 | 4 in | 3-3/4 in | 2 |
Rough and surfaced thicknesses: USDA Wood Handbook, Table 6–4. Board feet: our arithmetic.
Board feet in common lumber
| Lumber | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 1x4 | 2.67 | 3.33 | 4 | 5.33 |
| 1x6 | 4 | 5 | 6 | 8 |
| 1x12 | 8 | 10 | 12 | 16 |
| 2x4 | 5.33 | 6.67 | 8 | 10.67 |
| 2x6 | 8 | 10 | 12 | 16 |
| 2x8 | 10.67 | 13.33 | 16 | 21.33 |
| 2x10 | 13.33 | 16.67 | 20 | 26.67 |
| 2x12 | 16 | 20 | 24 | 32 |
| 4x4 | 10.67 | 13.33 | 16 | 21.33 |
Nominal sizes, as the Wood Handbook counts them.
Because hardwood comes in random widths, you can’t buy “ten 6 in boards” as easily as a stack of 2x4s. Work out the board feet your cut list needs, add an allowance for knots, checks and offcuts, and pick boards until the total is covered.
Questions people ask
How many board feet is a 2x4x8?
5.33 board feet: 2 × 4 × 8 ÷ 12.
How many board feet are in a 1x12x12?
12 board feet: 1 × 12 × 12 ÷ 12.
How many board feet is a 2x6x10?
10 board feet: 2 × 6 × 10 ÷ 12.
Do you use actual or nominal size for board feet?
Nominal thickness and width, with the actual length, for lumber 1 in or thicker. Thinner lumber counts as 1 in.
What does MBF mean?
A thousand board feet, the unit sawmills and lumber yards use for large orders.
How do I convert board feet to cubic feet?
Divide by 12. A board foot is 144 cubic inches and a cubic foot is 1,728, so 12 board feet make a cubic foot (about 0.0283 m³).
Sources
- USDA Forest Service, Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021): glossary (board foot), chapter 6 (hardwood lengths, Table 6–4 hardwood thicknesses, Table 6–6 softwood sizes from PS 20), abbreviations (MBF)
Checked October 12, 2026. Metric values: 1 board foot = 144 in³ = 2,359.7 cm³.