The board foot formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
A board foot is 144 cubic inches — a piece 1" thick, 12" wide and 1 ft long. The formula just counts how many of those fit in your board.
Worked examples
- One 2×6, 10 ft: 2 × 6 × 10 ÷ 12 = 10 board feet.
- Ten 2×4s, 8 ft: 2 × 4 × 8 ÷ 12 = 5.33, × 10 = 53.3 board feet.
- 8/4 walnut, 7" × 6 ft: 2 × 7 × 6 ÷ 12 = 7 board feet; at $14 per board foot, $98.
- All in inches — 1" × 8" × 30": 1 × 8 × 30 ÷ 144 = 1.67 board feet.
Board feet of common lumber
Nominal sizes, the way lumberyards count them.
| Size | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 1×4 | 2.67 | 3.33 | 4 | 5.33 |
| 1×6 | 4 | 5 | 6 | 8 |
| 1×8 | 5.33 | 6.67 | 8 | 10.67 |
| 1×12 | 8 | 10 | 12 | 16 |
| 2×4 | 5.33 | 6.67 | 8 | 10.67 |
| 2×6 | 8 | 10 | 12 | 16 |
| 2×8 | 10.67 | 13.33 | 16 | 21.33 |
| 2×10 | 13.33 | 16.67 | 20 | 26.67 |
| 2×12 | 16 | 20 | 24 | 32 |
| 4×4 | 10.67 | 13.33 | 16 | 21.33 |
| 6×6 | 24 | 30 | 36 | 48 |
Nominal vs actual size
A 2×4 actually measures 1 1/2" × 3 1/2", but dimensional lumber is sold by nominal size, so a 2×4×8 is billed as 5.33 board feet. Hardwood is sold rough by the quarter: 4/4 (1"), 5/4 (1 1/4"), 8/4 (2") — measure the width of each board, since hardwood comes in random widths.
Let the calculator do it
The board foot calculator adds up a whole lumber list with prices, and estimates board feet in logs by the Doyle, Scribner and International rules.