How to use the cutting stock board optimizer
- Enter the stock board length you buy, such as 96 for an 8 foot board measured in inches. Use one unit for every length on the page.
- Enter the saw kerf, the width of material the blade removes at each cut. The 0.125 shown is an example for a thin blade.
- List each piece length and how many you need. Add a row for every different length.
- Read the number of boards to buy, the cut list for each board and what is left over. Matching patterns are grouped, so "2 boards: 34 + 34 + 22.5" means two boards cut the same way.
Formula
length used on a board = sum of its pieces + kerf x (pieces - 1)
a board is valid when length used <= stock length
fewest boards possible by length alone = ceil(total of all pieces / stock length)
left over = boards x stock length - total of all pieces
With 12 pieces or fewer the tool tries every way of grouping them and returns a plan with the fewest boards. For longer lists it packs by first fit decreasing, which is quick but does not prove that nothing smaller exists.
Six pieces on 96 inch boards
Say you need pieces of 18, 46, 42, 34, 22 and 24 inches from 96 inch boards with a 0.125 inch kerf. A common shortcut, placing the longest piece first on the first board where it fits, puts 46 and 42 together, then 34, 24 and 22, and leaves 18 alone: 3 boards.
Trying every grouping finds 2 boards: 46 + 24 + 22 uses 92.25 inches including two kerfs, and 42 + 34 + 18 uses 94.25. The pieces total 186 inches, so 2 boards (192 inches) is the least that could ever work, and the exact search reaches it.
The starting example on the page has 14 pieces, so it uses first fit decreasing: 4 boards with 57 inches left over, where the total of the pieces (327 inches) already forces at least 4.
Why the kerf matters
A saw blade turns a strip of wood into dust at every cut. For a board cut into three pieces, two kerfs are lost between neighboring pieces. With a 0.125 inch kerf that is only a quarter inch, but it can decide whether 47.8 and 48 inch pieces share a 96 inch board (they do, with 0.075 to spare) or whether 47.9 and 48 do not (they need 96.025).
The tool counts one kerf between neighboring pieces on a board and none at the ends. If you square up a rough end, add a trim allowance to your piece lengths or reduce the stock length before you start.
Using the plan
Mark and cut the longest piece on each board first, then work down to the shortest, so a mistake costs a short piece and not a long one. Check the grain, knots and any pieces that must match each other before you commit to a plan, because the tool only knows lengths.
Once you know the boards to buy, price them by volume with the Board Foot Calculator, or use the Linear Feet Calculator when the lumber is sold by the foot.
More layout tools
For other layouts and cuts in the home and workshop, try the Plank Stagger Planner, Tile Layout Calculator and Beam Deflection Calculator.
Assumptions and limits
- Every stock board has the same length and every cut is straight across the board.
- One kerf is lost between neighboring pieces on a board and none at the ends.
- Pieces can be placed in any order and any piece can go on any board, with no grain or defect limits.
- Lengths are in one unit that you choose, and the tool never converts units.
Frequently asked questions
How do I work out how many boards I need for a cut list?
Add up every piece, divide by the board length and round up for a minimum, then pack the pieces onto boards allowing for kerf. The tool does the packing and shows the pattern for each board.
What is saw kerf and should I include it?
Kerf is the thickness of the cut made by the blade, often between 0.09 and 0.125 inch for a table saw. Include it, because several cuts on one board can use up an inch or more.
Is the answer always the fewest boards possible?
It is for up to 12 pieces, because every grouping is tried. For longer lists it uses first fit decreasing, which is usually within one board of the best plan but is not proven to be the smallest.
Can I cut from boards of different lengths?
Not in one run. Run the tool once for each stock length you can buy and compare the number of boards and the waste.