Lumber Calculator
Free lumber board foot calculator. Work out board feet and total cost for any thickness, width, and length. Compare hardwood prices by the board foot.
A board-foot calculator converts lumber dimensions into the volume unit sawmills and yards actually price: the board foot. Enter thickness, width, length, and quantity to get total board feet and the cost at your price per board foot.
The board-foot formula
One board foot is 1 inch thick by 12 inches wide by 12 inches long, which is 144 cubic inches of wood. Because this calculator takes length in feet, the divisor is 12:
board feet per piece = thickness (in) × width (in) × length (ft) ÷ 12
Total board feet is that figure multiplied by the number of pieces. Total cost is total board feet multiplied by the price per board foot. If you ever measure length in inches rather than feet, divide by 144 instead of 12.
Worked example: ten 2 × 4s, 8 feet long
Using the calculator’s defaults: thickness 2 in, width 4 in, length 8 ft, quantity 10, price $3.50 per board foot.
| Step | Calculation | Result |
|---|---|---|
| Nominal volume in inch-feet | 2 × 4 × 8 | 64 |
| Board feet per piece | 64 ÷ 12 | 5.33 bdft |
| Total board feet (10 pieces) | 5.33 × 10 | 53.33 bdft |
| Total cost at $3.50/bdft | 53.33 × $3.50 | $186.67 |
A single 2 × 4 × 8 is therefore 5.33 board feet, and a bundle of ten is 53.33 board feet. Lumber is priced on nominal size, so the 2 and 4 are the labelled dimensions even though the finished board measures about 1.5 × 3.5 inches.
Reference: board feet per 8-foot piece
| Nominal size | Board feet per 8-ft piece | 10 pieces |
|---|---|---|
| 1 × 4 | 2.67 | 26.67 |
| 1 × 6 | 4.00 | 40.00 |
| 1 × 8 | 5.33 | 53.33 |
| 1 × 12 | 8.00 | 80.00 |
| 2 × 4 | 5.33 | 53.33 |
| 2 × 6 | 8.00 | 80.00 |
| 2 × 8 | 10.67 | 106.67 |
| 2 × 10 | 13.33 | 133.33 |
| 2 × 12 | 16.00 | 160.00 |
| 4 × 4 | 10.67 | 106.67 |
Read a row across to see how a longer piece scales: double the length and you double the board feet, because length sits in the numerator.
Why nominal size is used for pricing
A two-by-four starts as a rough 2-inch by 4-inch piece, then is surfaced and dried down to about 1.5 by 3.5 inches. Lumber yards price the nominal size because it is the standard the whole trade quotes against. Plugging actual dimensions into the formula would understate the board feet by roughly a third for small stock, so keep the labelled numbers.
Board feet also make unlike pieces comparable. A 2 × 10 and a stack of 1 × 4s can only be priced on the same scale once both are converted to volume, which is exactly what this calculation does.
Common mistakes
- Mixing length units. Length in feet divides by 12; length in inches divides by 144. Confusing the two halves or doubles the answer.
- Measuring finished instead of nominal size. A “2 × 4” is priced as 2 × 4, not the actual 1.5 × 3.5.
- Forgetting waste. Buying exactly your net board feet leaves nothing for knots, warp, and miscuts. Add 10–15%.
- Treating linear feet as board feet. A 12-foot 1 × 4 and a 12-foot 2 × 12 are the same length but very different volumes.
How many board feet is a 2 × 4 × 8?
2 × 4 × 8 ÷ 12 = 5.33 board feet. Change the length and the figure scales directly: a 2 × 4 × 16 is 10.67 board feet.
Should I use nominal or actual dimensions?
Nominal. Lumber pricing uses the labelled size, so enter 2 and 4 for a two-by-four rather than the surfaced 1.5 and 3.5.
How much should I add for waste?
For framing and general construction, 10% is a common allowance. For hardwood with knots and defects, or a project with many short cuts, 15% is safer.
Is board feet used for plywood and sheet goods?
No. Sheet goods are sold by the sheet or by square footage, not board feet. This calculator is for solid sawn lumber such as framing stock and hardwood.
Board feet price the decking; the deck cost calculator adds framing and fasteners, and the concrete calculator sizes the footings that carry the frame.