How do I plan cuts from 6 m or 20 ft lengths?

Start with the parts longer than half a length: each one takes a bar of its own, so count those first, then fill the space beside them with the short parts. On 6000 mm stock with a 3 mm blade the line is 2998.5 mm; on a 20 ft (240 in) stick with a 1/8 in blade it is 119 15/16 in. Dividing the total length by the stock length ignores that line, and it undercounts on exactly the jobs where it matters.

The half-length trap, in millimetres

Six parts at 3100 mm and six at 1400 mm, from 6000 mm bars with a 3 mm blade. 27000 mm of parts plus 12 cuts is 27036 mm: 4.5 bars, so dividing says 5.

It takes 6, and that is proved optimal. No bar holds two 3100s, so there are six bars before a single 1400 is cut. The 1400s then fit in the space beside the 3100s, so the long parts set the count, not the total length. Cutting each size from its own bars is worse again: 8.

The same trap, in feet and inches

20 ft sticks (240 in) and a 1/8 in blade: four parts at 126 in (10′ 6″), four at 90 in (7′ 6″) and six at 46 in. 1140 in of parts is 4.75 sticks, so dividing says 5.

It takes 6, also proved optimal. Each 126 takes a stick of its own and pairs with a 90, leaving 23 3/4 in. The six 46s go three to a stick on the last two.

Is 6 m the right length to buy?

If your supplier sells other lengths, check before you order. The same 3100 and 1400 job on other stock:

On 6.5 m bars two 3100s fit with room to spare, and the job buys 3.5 metres less steel. On 12 m bars it buys the same 36 metres as on 6 m, in heavier bars, with 2988 mm left on each. There is no best stock length in general, only a best length for each cut list. Enter every length you can buy and the plan picks the mix that uses the least material; price them and the Cheapest method (Hobby plan) picks on money.

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