What is a board foot?
A board foot is the amount of wood in a board 1 inch thick, 12 inches wide and 1 foot long: 144 cubic inches, or one twelfth of a cubic foot. It is the most common unit for measuring lumber, logs and standing trees.
Source University of Kentucky Extension · FOR-9, A Landowner’s Guide: Measuring Farm Timber (board foot and Table 1) ↗NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
How to calculate board feet
Here it is with your numbers:
- Multiply the thickness, width and length, then divide by 12: 1 × 6 × 8 ÷ 12 = 4 board feet each.
- Multiply by the 10 pieces: 4 × 10 = 40 board feet.
It means you are buying 40 board feet of lumber.
Multiply the thickness and width in inches by the length in feet, then divide by 12. If you measure the length in inches too, divide by 144 instead. Multiply by the number of pieces for the whole stack, and by the price per board foot for the cost.
Source Oregon State University Extension · 4-H Wood Science glossary (board foot, nominal) ↗
Nominal or actual size?
Lumber is known by its nominal size, and the dry, planed board is smaller: a 2 × 4 is 1-1/2 × 3-1/2 inches, and a 1-inch board is 3/4 inch. Hardwood thickness is given in quarters of an inch of rough size: 4/4 is 1 inch rough and 13/16 inch once surfaced on both sides.
The board feet depend on which size is used, so ask your yard whether it bills on nominal, rough or actual sizes and type those. For rough hardwood, use the Rough lumber tally button.
| Quarters | Rough (in) | Surfaced (in) |
|---|---|---|
| 4/4 | 1 | 13/16 |
| 5/4 | 1-1/4 | 1-1/16 |
| 6/4 | 1-1/2 | 1-5/16 |
| 8/4 | 2 | 1-3/4 |
| 12/4 | 3 | 2-3/4 |
| 16/4 | 4 | 3-3/4 |
Board feet in common lumber sizes
Board feet in one board of each nominal size, by length.
| Size (in) | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 1 × 4 | 2.67 | 3.33 | 4.00 | 5.33 |
| 1 × 6 | 4.00 | 5.00 | 6.00 | 8.00 |
| 1 × 8 | 5.33 | 6.67 | 8.00 | 10.67 |
| 1 × 10 | 6.67 | 8.33 | 10.00 | 13.33 |
| 1 × 12 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2 × 4 | 5.33 | 6.67 | 8.00 | 10.67 |
| 2 × 6 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2 × 8 | 10.67 | 13.33 | 16.00 | 21.33 |
| 2 × 10 | 13.33 | 16.67 | 20.00 | 26.67 |
| 2 × 12 | 16.00 | 20.00 | 24.00 | 32.00 |
| 4 × 4 | 10.67 | 13.33 | 16.00 | 21.33 |
FAQs
How big is a board foot?
A board foot is 144 cubic inches of wood: a board 1 inch thick, 12 inches wide and 1 foot long. Any shape with the same amount of wood is also 1 board foot, such as a board 1 inch thick, 6 inches wide and 2 feet long.
Source Oregon State University Extension · 4-H Wood Science glossary (board foot, nominal) ↗
How long is a board foot?
A board foot is an amount of wood, not a length. How long it is depends on the board: a 1 × 12 is 1 board foot every foot, a 1 × 6 every 2 feet, and a 2 × 6 every foot.
How many board feet are in a square foot?
A square foot of board 1 inch thick is 1 board foot. Each extra inch of thickness adds one more, so a square foot of 2-inch lumber is 2 board feet.
How do you measure board feet?
Measure the thickness and width in inches and the length in feet, multiply them and divide by 12. For rough lumber, a board under 1 inch thick counts as 1 inch, a thicker one goes to the nearest quarter inch, and the width usually to the nearest inch.
Sources
- University of Kentucky Extension: FOR-9, A Landowner’s Guide: Measuring Farm Timber (board foot and Table 1)
- Oregon State University Extension: 4-H Wood Science glossary (board foot, nominal)
- USDA Forest Service, Forest Products Laboratory: Wood Handbook (2021), Chapter 6: Commercial Lumber
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement