To know how much lumber to buy, list every piece your project needs, then fit those pieces into the board lengths the yard sells. A simple workbench frame of twelve 2x4 pieces (four 33 in legs, four 57 in rails, four 21 in rails) fits into two 16 ft boards and one 8 ft board, 40 feet of 2x4, with every offcut shown in the cutting diagram.
How the lumber takeoff works
The calculator groups your cuts by nominal size, since a 2x4 can only come from a 2x4. For each size it:
- sorts the cuts longest first,
- packs them into boards, leaving one saw kerf between neighbouring cuts,
- tries every single board length you allow and a mixed plan that picks, for each new board, the length the remaining cuts fill best,
- shortens every board to the shortest stock length that still holds its cuts,
- keeps the plan with the least total length bought, then the one with fewer boards.
Board feet = nominal thickness (in) × nominal width (in) × length bought (ft) ÷ 12
The board feet use the nominal size, as the American Softwood Lumber Standard (PS 20-25, section 2.2) defines board measure, even though a dry 2x4 measures 1½ × 3½ inches (PS 20-25, Table 3). Lengths come in multiples of 1 or 2 feet (PS 20-25, section 5.3.1), and the standard trims boards to no less than their nominal length, so an 8 foot board really gives you 8 feet of cuts.
Worked example: a workbench
The defaults describe a 2x4 workbench frame with a 2x6 top:
| Cut | Size | Pieces | Length |
|---|---|---|---|
| Legs | 2x4 | 4 | 33 in |
| Long rails | 2x4 | 4 | 57 in |
| Short rails | 2x4 | 4 | 21 in |
| Top boards | 2x6 | 4 | 60 in |
The twelve 2x4 cuts add up to 444 inches, 37 feet. With a ⅛ in kerf the calculator packs one 16 ft board with a rail and four legs, a second 16 ft board with three rails, and an 8 ft board with the four short rails: 40 feet of 2x4. The four 60 in top boards go two to a 12 ft 2x6, so two 12 ft 2x6s, 24 board feet.
The waste field defaults to 10%. The cutting plan already counts every offcut, so this allowance only buys spare boards against a split end or a miscut: 10% of 40 feet is 4 feet, so one spare 8 ft 2x4, and one spare 8 ft 2x6. The shopping list becomes two 16 ft and two 8 ft 2x4s, and two 12 ft and one 8 ft 2x6: 64 board feet in all. Set the waste to 0 when you trust your stock.
Nominal vs actual lumber sizes
| Nominal | Actual (dry) | Board feet per ft |
|---|---|---|
| 2x4 | 1½ × 3½ in | 0.67 |
| 2x6 | 1½ × 5½ in | 1 |
| 2x8 | 1½ × 7¼ in | 1.33 |
| 2x10 | 1½ × 9¼ in | 1.67 |
| 2x12 | 1½ × 11¼ in | 2 |
| 4x4 | 3½ × 3½ in | 1.33 |
| 6x6 | 5½ × 5½ in | 3 |
Actual sizes are PS 20-25, Table 3 (timbers 5 in and larger lose ½ in each way). Design with the actual size: two 2x4 rails stacked are 7 inches, not 8.
Which board lengths to buy
Longer boards often pack better, but they are harder to haul and not every store stocks them. Choose 8, 12 and 16 ft or a single length in the list if that is what your store stocks; the plan and the board feet update. A cut longer than the longest board is flagged, since it would need a splice.
Kerf matters when many short pieces come from one board: eight cuts with a ⅛ in blade eat an inch. Set 0 if you ask the yard to cut for you.
Price
Lumber yards quote framing lumber per board foot or per thousand board feet (MBF). Enter a price per board foot and the calculator multiplies it by the board feet bought, spares included. For a home center that prices by the piece, divide the shelf price by the board feet of that piece to compare.
What to work out next
- A wall rather than a bench: the stud calculator and the framing calculator count studs, plates and headers from the wall length.
- Hardwood priced by the board foot: the board foot calculator handles 4/4 and 8/4 stock.
- Shelves, backs and cabinet boxes: the plywood calculator optimizes a cut list on 4 × 8 sheets.
- A deck surface: the deck board calculator.
All wood tools live under framing and lumber.