How it works
The formula
= thickness × width × length (all in inches) ÷ 144
Assumptions
- A board foot is 144 cubic inches: a piece 1 in thick, 12 in wide and 1 ft long.
- Lumber is tallied on its nominal size, not the planed size you measure: a 2×4 counts as 2 × 4 in even though it's 1-1/2 × 3-1/2 in. Hardwood is sold by rough thickness in quarters of an inch: 4/4 is 1 in, 8/4 is 2 in.
- Most softwood framing lumber at home centers is priced per piece, not per board foot; hardwood and lumberyard boards are priced per board foot.
Worked example
Ten 2×6 boards, 8 ft long
- One board: 2 × 6 × 8 ÷ 12 = 8 board feet
- Ten boards: 8 × 10 = 80 board feet
- At $6.50 a board foot: 80 × 6.50 = $520
Board feet per piece
| Nominal size | 8 ft | 10 ft | 12 ft |
|---|---|---|---|
| 1 × 4 | 2.67 | 3.33 | 4 |
| 1 × 6 | 4 | 5 | 6 |
| 1 × 8 | 5.33 | 6.67 | 8 |
| 1 × 12 | 8 | 10 | 12 |
| 2 × 4 | 5.33 | 6.67 | 8 |
| 2 × 6 | 8 | 10 | 12 |
| 2 × 8 | 10.67 | 13.33 | 16 |
| 2 × 10 | 13.33 | 16.67 | 20 |
| 2 × 12 | 16 | 20 | 24 |
| 4 × 4 | 10.67 | 13.33 | 16 |
| 6 × 6 | 24 | 30 | 36 |
Hardwood thickness in quarters
| Quarters | Rough thickness | Board feet per sq ft of board |
|---|---|---|
| 4/4 | 1 in | 1 |
| 5/4 | 1.25 in | 1.25 |
| 6/4 | 1.5 in | 1.5 |
| 8/4 | 2 in | 2 |
| 12/4 | 3 in | 3 |
| 16/4 | 4 in | 4 |
Questions people ask
How do you calculate board feet?
Multiply thickness by width in inches, multiply by the length in feet, and divide by 12. A 2×6 that's 8 ft long is 2 × 6 × 8 ÷ 12 = 8 board feet. With every size in inches, divide by 144 instead.
How many board feet in a 2×4?
An 8 ft 2×4 is 5.33 board feet, a 10 ft one 6.67 and a 12 ft one 8. Board feet use the nominal 2 × 4 in size, not the actual 1-1/2 × 3-1/2 in.
Why use nominal size and not the actual size?
Board feet are counted on the size the board was cut to before drying and planing, so a "1 in" board counts as 1 in even if it measures 3/4 in. That's the trade convention; when buying surfaced hardwood, ask whether the price is on rough or finished size.
What does 4/4 or 8/4 lumber mean?
Hardwood thickness in quarters of an inch, rough-sawn: 4/4 ("four quarter") is 1 in, 5/4 is 1-1/4 in, 8/4 is 2 in. After planing, 4/4 is usually about 13/16 in thick.
How many board feet in a cubic foot?
12. A cubic foot is 1,728 cubic inches and a board foot is 144.