What Is a Board Foot?
Definition
A board foot is a unit of lumber volume equal to 144 cubic inches. The reference shape is a board one inch thick, twelve inches wide, and one foot long. Any piece that adds up to 144 cubic inches is one board foot, whether it is 1x12x1ft, 2x6x1ft, or 1x6x2ft.
Why lumber uses volume, not length
Rough hardwood comes in random widths and lengths. Pricing by the piece would be unfair, and pricing by length ignores how wide or thick a board is. Volume is the honest measure, so hardwood dealers price by the board foot and you pay for the wood you actually get.
The formula
board feet = (thickness x width x length in inches) / 144
Or, when length is in feet:
board feet = (thickness x width x length in feet) / 12
Quick reference
| Board | Board feet |
|---|---|
| 1 x 4 x 8 ft | 2.67 |
| 1 x 6 x 8 ft | 4 |
| 1 x 12 x 8 ft | 8 |
| 2 x 4 x 8 ft | 5.33 |
| 2 x 6 x 8 ft | 8 |
| 4 x 4 x 8 ft | 10.67 |
Nominal size
Board feet are figured at nominal size, the size lumber is named and sold by. A planed 2x4 measures about 1.5 by 3.5 inches, but it is still counted as a full 2 by 4. Use the nominal numbers so your math matches the invoice.
Frequently asked questions
- What is one board foot?
- 144 cubic inches of wood, the same as a board 1 inch thick, 12 inches wide, and 1 foot long.
- How many board feet is a 2x4x8?
- 5.33 board feet. Multiply 2 by 4 by 8 and divide by 12.
- Is a board foot a measure of area?
- No, it is a measure of volume. Square feet measure surface area; board feet include thickness.
- Why is my planed board smaller than nominal?
- Surfacing removes material. A board is figured and priced at its nominal, pre-planing size even though it measures smaller.