Cut List Optimiser

Cut List Optimiser — frequently asked questions

Why is the count higher than the total length divided by the stock?

Because material does not flow. Dividing assumes every bar can be filled to the last millimetre and that offcuts can be welded end to end. In practice a 6 m length holds two 2.4 m pieces and 1.2 m goes on the rack, so five pieces need three lengths rather than the two the division suggests. The gap between those two numbers is the reason this tool exists.

Does the plan it gives me use the fewest possible lengths?

Not provably. Deciding the true minimum is an NP-hard problem, and solving one for eighty pieces is not something to do while standing at a merchant's counter. This uses first-fit-decreasing, the standard heuristic, which is known never to need more than about 11/9 of the optimum plus a constant. In ordinary cut lists it usually finds the optimum outright; where it does not, it is over by one length. It is stated rather than hidden because 'good' and 'proven best' are different claims.

How much does the saw kerf actually matter?

Enough to change the order. Every piece taken off a bar costs one pass of the blade, and at 3 mm a bar cut into eight pieces loses 24 mm — which is exactly the amount by which the last piece fails to fit. The kerf is charged per piece here, which over-counts by at most one cut per bar, the case where the last piece runs to the very end. That errs toward having enough material, which is the direction an estimate should err.

What happens to a piece longer than the stock length?

It is listed on its own and kept out of the count. It cannot be cut from one length, so it needs either a longer stock size or a joint — and where a joint falls in a loaded member is a structural decision, not a packing one. A plan that quietly split it across two bars would hand you a cheaper order and a hidden splice.

Can I give it more than one stock length at a time?

No — one stock length per run. That is a real limit rather than an oversight: choosing between a 6 m bar and a 7.5 m bar is a purchasing question with a price attached, and the honest way to answer it here is to run the list twice and compare the bar count and the waste percentage. The cheaper bar is often not the cheaper job.

Does the order I type my pieces in change the plan?

No. The pieces are sorted longest-first before anything is packed, which is the 'decreasing' half of first-fit-decreasing, so a list typed in the order you walked the drawing gives exactly the same plan as one typed neatly. Type them as you find them.

Should I add anything for splits, crook and damaged ends?

Yes, and the plan will not do it for you. Every bar here is assumed perfect from end to end, which is true of steel from a stockholder and optimistic about timber off a rack. Trim allowances at the factory ends, a bowed length you end up ripping, and the piece somebody cuts wrong are all real and none of them are in the packing. Add them as extra pieces on the list rather than as a percentage, so they get packed like everything else.

What do I do with the offcuts it leaves?

Read them off the plan before you cut, because it shows the remainder left on each individual bar rather than just a total. One bar with a 1.8 m drop is a future piece worth racking; six bars with 300 mm each are firewood, and the same total waste percentage covers both. That distinction only exists per bar, which is why the plan is printed bar by bar.

Turn this measurement into a quantity

A reading on its own does not order material. These calculators take what you just measured and give you quantities, cuts or cost.

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