How it works
The pieces go in longest first, each into the length it fits best, leaving the least over; a new length is only started when nothing bought has room, and each length is then the shortest that still holds its pieces. Two ways of starting are tried (with the longest lengths, and with the shortest that fit), and the one that buys less timber is kept.
The saw cut is taken between every two pieces on a length, and the trim from each end. A piece longer than the longest length is joined from parts, none shorter than 300 mm.
For skirting and architrave round a room, see how much skirting and architrave do I need, and for a stud wall's studs and noggins, stud wall spacing.
Questions
How does it choose which lengths to buy?
Longest pieces first, each into the length where it leaves the least over, starting a new length only when none has room. Each length is then the shortest that still holds its pieces. It tries this starting with the longest lengths and with the shortest that fit, and keeps whichever buys less timber.
What if a piece is longer than the longest length?
It's made from parts joined end to end, as long as the longest length, with no part shorter than 300 mm, so there are no slivers to join. The answer says how many joins there are.
What should I put for the trim?
How much you cut off each end of a length before using it: ends are often split, out of square or marked. Leave it at 0 for clean ends.
Which lengths should I type?
The ones your merchant sells that timber in. In the UK that's usually 1.8 m to 4.8 m in steps of 0.6 m, or 5.4 m for longer stock; in America 8, 10, 12, 14 and 16 ft. Leave out any your merchant doesn't stock.
Is this the same as JoinerKit's cutting list?
Yes. It's the same code that works out the timber for skirting, architrave, stud walls, panelling and frames in JoinerKit, where the pieces come from what you draw.