The method in three steps
- Measure the thickness and width in inches, and the length in feet.
- Multiply the three numbers.
- Divide by 12. If you measured the length in inches, multiply the three numbers in inches and divide by 144.
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
Worked examples
| Board | Calculation | Board feet |
|---|---|---|
| 1 in × 6 in × 8 ft | 1 × 6 × 8 ÷ 12 | 4.00 |
| 2 in × 4 in × 10 ft | 2 × 4 × 10 ÷ 12 | 6.67 |
| 1-1/4 in × 7 in × 9 ft | 1.25 × 7 × 9 ÷ 12 | 6.56 |
| 2 in × 12 in × 16 ft | 2 × 12 × 16 ÷ 12 | 32.00 |
| 1 in × 8 in × 54 in | 1 × 8 × 54 ÷ 144 | 3.00 |
Turn a fraction into a decimal before you multiply: 1-1/4 is 1.25, 1-1/2 is 1.5 and 3/4 is 0.75.
A stack of boards
For a run of boards that are all the same size, do one and multiply by the count. Ten 1x6 boards at 8 ft are 10 × 4 = 40 board feet. When the sizes are mixed, work out each board and add them up.
Say you need 6 boards of 1x8x10 and 4 boards of 2x4x8:
| Boards | Each | Total |
|---|---|---|
| 6 × 1x8x10 | 6.67 | 40.00 |
| 4 × 2x4x8 | 5.33 | 21.33 |
| Total | 61.33 |
Hardwood and the quarter system
Rough hardwood thickness is quoted in quarters of an inch. 4/4 is 1 inch, 5/4 is 1-1/4 inches, 6/4 is 1-1/2 inches and 8/4 is 2 inches. A 4/4 board 8 inches wide and 10 ft long is 1 × 8 × 10 ÷ 12 = 6.67 board feet. The same board in 8/4 doubles to 13.33.
Softwood and nominal size
Construction lumber is counted by its nominal size, so a 2x4 counts as 2 × 4 even though the real board is 1-1/2 by 3-1/2 inches. An 8 ft 2x4 is 5.33 board feet. The lumber dimensions chart has the real sizes.
Allow for waste
The formula gives you the board feet in the pieces you listed, not what you should buy. Defects, cuts and offcuts all eat into a board, so buy more than the net total. A furniture project usually wants 20 to 30% extra, and simple framing cuts need less.
Skip the arithmetic with the board foot calculator, convert a store price with the lumber cost calculator, or read what a board foot is for where the unit comes from.
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12.
How do you calculate board feet with the length in inches?
Multiply thickness, width and length, all in inches, and divide by 144.
How many board feet are in a 1x6x8?
4 board feet.
How many board feet are in a 2x4x8?
5.33 board feet, using the nominal size.
What does 8/4 mean on hardwood?
The board is 2 inches thick when rough, because the number is the thickness in quarters of an inch.
Should I use nominal or actual size?
For lumber priced by the board foot, use the nominal size, because that is how it is sold.