Quick answer: list every piece and its length, fit the pieces onto stock boards longest-first (allowing ⅛ in per cut), and count the boards. Often a 10 or 12 ft board wastes less than an 8 or 16 ft one; the calculator checks every length for you.
How the lumber calculator works
Most lumber calculators simply add up length and divide by the board length. That underestimates, because offcuts that are too short to use are wasted. This one plans the cuts the way a carpenter would:
- It sorts your pieces from longest to shortest.
- It places each piece on the first board that still has room, allowing one saw kerf per cut (first-fit decreasing).
- It starts a new board when no existing board has room.
- It repeats this for every stock length and shows which uses the fewest linear feet.
The result is a cutting plan you can take to the saw: each bar is one board, each yellow block is a cut, and the striped end is the offcut.
Choosing stock lengths
Longer boards are not always better. Pieces that are just over half a board length waste nearly half of every board. The trick is to pick a length that is close to a multiple of your common pieces. Some quick guides:
| Piece length | Fits on 8 ft | Fits on 10 ft | Fits on 12 ft | Fits on 16 ft |
|---|---|---|---|---|
| 24 in | 3 (+ 24 in offcut) | 4 (+ 24 in offcut) | 5 (+ 24 in offcut) | 7 (+ 23 in offcut) |
| 30 in | 3 | 3 (+ 30 in offcut) | 4 (+ 24 in offcut) | 6 (+ 11 in offcut) |
| 36 in | 2 (+ 24 in offcut) | 3 (+ 12 in offcut) | 3 (+ 36 in offcut) | 5 (+ 12 in offcut) |
| 48 in | 1 (+ 48 in offcut) | 2 (+ 24 in offcut) | 2 (+ 48 in offcut) | 3 (+ 48 in offcut) |
| 60 in | 1 (+ 36 in offcut) | 1 (+ 60 in offcut) | 2 (+ 24 in offcut) | 3 (+ 12 in offcut) |
With a ⅛ in kerf, exact fits like 4 × 24 in on an 8 ft board don’t quite work; factory ends are also often rough, so plan to trim ½ in off each end.
Worked example: a bookshelf
A bookshelf from 1×12 boards needs two 72 in sides and five 34½ in shelves. These are the calculator’s starting values.
- 8 ft boards: each side needs its own board (only 24 in is left, too short for a shelf), and the five shelves need three more: 5 boards = 40 lin ft, 66% yield.
- 10 ft boards: a side and a shelf fit on each of two boards, and three shelves on the third: 3 boards = 30 lin ft, 88% yield.
- 12 ft boards: a side and two shelves on each of two boards, one shelf on a third: 3 boards = 36 lin ft.
Buying 10 ft boards saves two boards and 10 linear feet compared with 8 ft, just by choosing a different length.
Linear feet, board feet and pieces
- Pieces: how big-box stores price lumber (per 2×4 × 8 ft, for example).
- Linear feet: total length, used for trim, molding, decking and some lumber yards.
- Board feet: volume (T × W × L ft ÷ 12), used for hardwood and bulk softwood. See the board foot calculator.
Enter the price in whichever unit your store uses; the calculator converts using the lumber size you picked.
Quick take-offs for common projects
| Project | How to work it out |
|---|---|
| Wall framing | Use the framing calculator: studs, plates and headers |
| Deck boards | Deck width ÷ (board width + gap) = rows; each row × deck length |
| Deck joists | Deck length ÷ spacing + 1, each as long as the joist span |
| Fence rails | Rails per section × number of sections, cut to post spacing |
| Raised garden bed | Perimeter × number of board rows; cut two long and two short per row |
| Shelving | Sides, shelves, top and bottom as a cut list, like the example above |
Lumber sizes and grades
Nominal sizes are bigger than the actual board: a 2×4 is 1½ × 3½ in, a 1×12 is ¾ × 11¼ in. For appearance work, pick clear or select grades with few knots; for framing, No. 2 and better or stud grade is usual. Pressure-treated lumber is needed for ground contact and for plates on concrete.
How to make a cut list
- Draw the project and label every part (sides, shelves, rails, legs).
- Write the finished size of each part: thickness, width and length.
- Group parts by lumber size, so all 1×12 parts go in one list and all 2×4 parts in another. Run the calculator once per size.
- Add allowances: about ½ in in length for trimming rough ends, more if you will joint and plane.
- Enter the parts with their quantities and compare stock lengths.
How heavy is lumber?
Weight matters when you carry boards up stairs or load a trailer. Kiln-dried softwood framing lumber weighs roughly 25–35 lb per cubic foot, so a 2×4 × 8 ft (about 0.29 cu ft actual) weighs around 8–10 lb, and a 2×12 × 16 ft around 45–60 lb. Pressure-treated lumber is heavier when it is still wet from treatment, and hardwoods such as oak are heavier still.
Common mistakes
- Dividing total length by board length without planning cuts, which under-orders.
- Ignoring kerf on long cut lists: 20 cuts at ⅛ in lose 2½ in.
- Assuming square, clean factory ends; trim them first.
- Mixing sizes in one plan; plan each lumber size separately.
Notes for carpenters
Cut longest first. Cut the long pieces from the best boards first, then fill offcuts with short parts. That is exactly what the plan shows.
Defects. The optimizer assumes clear boards. Look at each board and move cuts around knots and checks; that is what the spare allowance is for.
Label offcuts. Keep offcuts over about 12 in; they become blocking, cleats and test pieces.
Optimizer limits. First-fit decreasing is near-optimal for typical cut lists, but not guaranteed perfect. On large orders, try a second stock length for the leftover pieces.
Tips
- Check transport: 16 ft boards may not fit in your vehicle; the yard can often cut them for you.
- Print the plan and tape it to the saw using Print under the result.
- Send the list to the yard with WhatsApp or Email.
Frequently asked questions
How do I calculate how much lumber I need?
List every piece you need to cut with its length and quantity. Then fit the pieces onto stock boards (8, 10, 12 or 16 ft), allowing about ⅛ in per saw cut, and count the boards. The calculator does the fitting for you and compares stock lengths.
What length of lumber should I buy?
The length that wastes the least once your cuts are laid out, which is not always the longest. For two 72 in sides and five 34½ in shelves, 10 ft boards need 3 boards (30 ft), while 8 ft boards need 5 (40 ft). The comparison table shows this for your cut list.
How do I calculate linear feet of lumber?
Add up the lengths of all the boards and divide inches by 12. Ten 8 ft boards are 80 linear feet. Linear feet ignore width and thickness; for volume use board feet.
What is kerf?
The width of wood the saw blade turns into sawdust, usually about ⅛ in for a circular or miter saw blade and less for thin-kerf blades. Each cut uses up one kerf, so long cut lists need a little extra length.
What lengths does lumber come in?
Dimensional lumber is commonly stocked in 2 ft steps from 8 to 16 ft, and often up to 20 ft or more for larger sizes. Studs also come in precut lengths such as 92⅝ and 104⅝ in.
How much extra lumber should I buy?
Once the cut list is planned, 5–10% extra covers splits, knots and mistakes. Without a plan, framers often add 10–15%.
What is the difference between linear feet and board feet?
Linear feet measure length only. Board feet measure volume (1 in × 12 in × 12 in). A 2×4 × 8 ft is 8 linear feet and 5.33 board feet.