Where the kerf actually goes
The single most common cut list error is counting the kerf once per piece instead of once per cut. If you take four pieces out of one stick, you make three cuts, because the fourth piece is whatever is left. Four pieces of 24 inches out of a 96 inch board is not four pieces; it is three pieces at 24 and one at 23 and five eighths, because a standard 1/8 inch blade removed three eighths of an inch on the way through. That is the whole reason this page exists, and it is why the calculator adds kerf between pieces on a stick rather than to every piece.
Kerf width depends on the blade, not the material. A thin-kerf 7-1/4 inch circular blade removes about 0.094 inches. A standard 10 inch table saw blade removes about 0.125. A track saw is often near 0.087, a bandsaw with a 1/2 inch blade can be under 0.035, and a chop saw cutting steel takes considerably more. Measure it once if it matters: cut a piece, measure the two halves, and the difference from the original is your kerf.
What first fit decreasing does, and what it does not
This is a bin packing problem, and bin packing is one of the classic problems with no efficient exact solution. Finding the provably minimum number of stock lengths for an arbitrary cut list means, in the worst case, checking an enormous number of arrangements. What this page does instead is a heuristic called first fit decreasing: sort every piece longest to shortest, then take them in that order and drop each into the first stick that has room for it, opening a new stick only when none of the existing ones can take it.
That approach is fast, it is easy to follow at the saw, and in practice it lands on the optimum or within one stick of it for most real cut lists. It is not a proof. There are lists where a different arrangement uses fewer sticks, and this page will not find them or warn you about them. If you are cutting something expensive and the answer sits right on the boundary between two stick counts, it is worth spending five minutes with a pencil trying to pack the offcuts differently before you buy the extra length.
Reading the layout
Each line under Layout is a pattern rather than a specific board. Stick x 3 followed by three lengths means three of your sticks get cut the same way. Cut them in the order shown, longest first, and the offcut is what is left at the end. Working longest to shortest on each stick is not just tidier: it means the small awkward pieces come out of a shorter remaining length, which is easier to handle safely on a mitre saw than balancing a full eight foot board for a two inch cut.
The offcut figure is per stick and it is worth glancing at before you start. A stick with a 30 inch offcut is a stick you should set aside intact rather than chop up, because it is future stock. A stick with a 1/4 inch offcut means the layout is tight and a lazy pencil line will cost you a piece.
End trim, defects and the pieces this cannot see
The end trim field removes a fixed amount from every stick before anything is laid out. Use it for factory ends that are split or painted, for squaring the first end, or as a general safety margin on rough stock. What it cannot do is handle defects in the middle of a board, because those are specific to the individual piece in front of you. Knots, checks, wane and bow are the reason lumber yields in real work run below what any calculator predicts, and the usual trade answer is to buy an extra stick rather than model it.
Grain direction and appearance are also outside this. If the four legs of a table need to come from matching stock, or a face frame needs the show face oriented a particular way, the packing that uses the fewest sticks may not be the packing you want. Optimise for material when material is the constraint, and optimise for appearance when it is not.
Buying to the layout
One thing worth trying before you commit: change the stock length and watch the stick count. Cut lists that waste a lot on one stock length often fit almost perfectly on another, because the arithmetic of what divides evenly changes completely. If your supplier stocks 8, 10, 12 and 16 foot lengths, run all four and compare not the stick count but the total money and the total offcut. The cheapest option is frequently not the one with the fewest sticks, and occasionally the longest stock is worse than the shortest because you are paying for offcut you will never use.
Questions people ask
Why does the calculator sometimes need one more stick than I expected?
Two likely reasons. The first is kerf: pieces that appear to divide evenly into the stock never quite do once the blade takes its share, so four 24 inch pieces do not come out of a 96 inch board. The second is that the heuristic packs greedily, longest first, and on some lists that leaves a gap a different arrangement would have filled. If your own arrangement genuinely fits in fewer sticks, use yours. The calculator is a starting point, not an authority.
How do I enter the cut list?
One piece per line, as a length, then optionally the letter x and a quantity, then optionally a name. So 36 x 4 legs means four pieces of 36 units each. A line with only a number, like 30, means one piece of 30. Blank lines are ignored, and lines starting with a hash are ignored so you can leave yourself notes. Everything must be in the same unit you selected at the top; the calculator does not parse feet and inches inside the list. If you work in feet and inches, enter decimal inches, so 6 feet 4-1/2 inches is 76.5.
Should I include a waste allowance on top of this?
Usually yes, and the calculator deliberately does not add one for you. This tells you the theoretical requirement given perfect stock and perfect cuts. Real stock has splits, bow and knots you will cut around, real measurements go wrong, and one piece per project gets cut on the wrong side of the line. On dimensional lumber for rough framing, buying one extra stick per ten is a common habit. On expensive hardwood, people usually buy to the calculation and then buy carefully, choosing boards at the yard against the specific pieces they need.
Does this work for metal, pipe and extrusion?
Yes, the arithmetic is identical for anything sold in fixed lengths and cut across. Switch the units to millimetres for aluminium extrusion and steel tube, which is how they are almost always specified. The one thing to adjust is the kerf, because an abrasive chop saw or a cold saw removes considerably more than a woodworking blade, often 1.5 to 3 mm. For pipe cut with a tubing cutter the kerf is effectively the wall being displaced rather than removed, and setting kerf to zero is closer to the truth than any woodworking figure.
Can I use it for sheet goods like plywood?
No, and it would give you a wrong answer if you tried. This solves a one dimensional problem: pieces cut across a stick, where only length matters. Sheet goods are a two dimensional problem where the width of each piece and the direction of every cut both matter, and the packing is a completely different exercise. Use this for boards, bars, tube, trim, extrusion and anything else where you only care about how long the pieces are.