Lumber Calculator
Lumber is sold by the piece in standard lengths, so a project's real question is how many boards of which length. Enter the total linear feet you need, or the length and number of identical pieces to cut, then the size and the stock length you'll buy. The calculator returns the boards, the offcut left on each one, the board feet and the cost at your price per board.
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Worked example: 240 linear feet of 2x6
| Step | Working | Result |
|---|---|---|
| Add 10% waste | 240 × 1.10 | 264 ft |
| 12 ft boards | 264 ÷ 12 | 22 boards |
| Board feet | 22 × (2 × 6 × 12 ÷ 12) | 264 bf |
Worked example: 30 pieces at 40 in
| Board | Pieces per board | Boards for 30 | Offcut each |
|---|---|---|---|
| 8 ft | 2 | 15 | 15.875 in |
| 10 ft | 2 | 15 | 39.875 in |
| 12 ft | 3 | 10 | 23.75 in |
| 16 ft | 4 | 8 | 31.625 in |
With a 1/8 in kerf a 10 ft board gives no more 40 in pieces than an 8 ft board: three pieces and two cuts need 120¼ in. That is why the cut list counts pieces per board rather than dividing total length — dividing would have ordered 9 ten-foot boards for 100 ft of pieces and come up short.
Nominal vs actual size
| Nominal | Actual (dry, dressed) | Board feet per 12 ft board |
|---|---|---|
| 1x4 | 0.75 × 3.5 in | 4 |
| 1x6 | 0.75 × 5.5 in | 6 |
| 1x8 | 0.75 × 7.25 in | 8 |
| 2x4 | 1.5 × 3.5 in | 8 |
| 2x6 | 1.5 × 5.5 in | 12 |
| 2x8 | 1.5 × 7.25 in | 16 |
| 2x10 | 1.5 × 9.25 in | 20 |
| 2x12 | 1.5 × 11.25 in | 24 |
| 4x4 | 3.5 × 3.5 in | 16 |
| 6x6 | 5.5 × 5.5 in | 36 |
Lumber is named by its nominal size and planed smaller: a 2x4 is 1½ × 3½ in. Board feet are still tallied on the nominal size. In the US and Canada boards come in 6 to 24 ft in 2 ft steps; 8–16 ft are the lengths most yards keep in stock.
Pricing by volume? The board foot calculator converts a list into board feet. For a whole deck frame, the deck framing calculator and deck joist calculator count joists, beams and rim boards, and the deck materials calculator builds the full list.
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Frequently asked questions
- How do I calculate how much lumber I need?
- Add up the linear feet of each size, add 10% for waste, and divide by the board length you'll buy. 240 linear feet of 2x6 in 12 ft boards is 240 × 1.10 ÷ 12 = 22 boards. For identical pieces, count how many fit on each board instead.
- How many pieces can I cut from one board?
- Divide the board length plus one saw kerf by the piece length plus one kerf, and round down. With a 1/8 in kerf, an 8 ft (96 in) board gives two 40 in pieces with 15⅞ in left over, and a 12 ft (144 in) board gives three with 23¾ in left. Three 48 in pieces won't come out of a 12 ft board: the two cuts take the extra ¼ in.
- What lengths does lumber come in?
- In the US and Canada the standard lengths are 6, 8, 10, 12, 14, 16, 18, 20, 22 and 24 ft. Most yards stock 8–16 ft in common sizes; the longer lengths are usually special-order and cost more per foot.
- How big is a 2x4 really?
- 1½ × 3½ in when dry and dressed. Lumber is named by its nominal size: a 2x6 is 1½ × 5½ in, a 2x8 1½ × 7¼, a 2x10 1½ × 9¼, a 2x12 1½ × 11¼ and a 4x4 3½ × 3½ in.
- Should I buy 8 ft or longer boards?
- Whichever wastes least for your pieces. For 40 in pieces an 8 ft board yields two (15⅞ in left) but a 10 ft board also yields only two, because three pieces plus two kerfs need 120¼ in. Twenty pieces take ten 8 ft boards (80 ft) or seven 12 ft boards (84 ft), so compare the price per board — the cut list shows the offcut for each length.
