What lengths does timber come in, and can I buy it cut to size?

The 300mm step is a hangover from imperial foot lengths and it is why timber comes in what look like arbitrary sizes. Knowing the ladder matters because your cutting list should be designed round it, and because whether the merchant will cut for you decides how you get it home.

Step by step

1. Learn the standard ladder.Softwood carcassing and PAR are normally stocked at 1.8, 2.1, 2.4, 2.7, 3.0, 3.3, 3.6, 4.2 and 4.8 metres, though not every yard carries every step in every section. Sheet-material battens and mouldings are often stocked in shorter lengths as well.
2. Check what your specific section is stocked in.Large sections tend to be stocked long and small ones short. A 47 by 225 joist may only be available from 3.6 metres upwards; a 25 by 50 batten may only come in 2.4. Ask before you plan a cutting list round a length that does not exist.
3. Design your cutting list round the ladder.Pieces that divide neatly into a stock length waste almost nothing; pieces that are slightly over half a stock length waste almost half. Where you have freedom over a dimension, choosing one that divides well into 2.4 or 3.6 metres is free money.
4. Ask for a cut to make it transportable.Nearly every merchant will cut a long length in half or into a few pieces so it goes in your car, usually free. This is a rough cut on a chop saw or a circular saw and it is not to a fine tolerance, so cut generously and trim at home.
5. Ask about a cutting service if you want accuracy.Some yards, and most sheds with a panel saw, will cut to a specified size for a per-cut charge. Timber cutting is less common and less accurate than sheet cutting, and the tolerance depends entirely on who is operating the saw. Ask what tolerance they work to before relying on it.
6. Ask about ordering cut to length.For a large order in a common section, a merchant may be able to supply cut to your lengths from the mill. It is worth asking on a big job. For a handful of pieces, it will not be offered.
7. Always leave yourself a trim allowance.Add 20 to 50mm to any cut you are relying on somebody else to make, and to any piece with end checks. Cutting a piece 10mm too long is a two-minute fix; 2mm too short is a new length.

Tips

• Buying longer and cutting down is usually cheaper per metre and always wastes less, provided you can get it home. Weigh that against the transport problem before ordering.
• If the merchant cuts for you, watch the cut being made and check both pieces before you leave. A cut made from the wrong end is not something you can fix in the car park.
• Mouldings, architrave and skirting are usually stocked in different lengths again, often up to 4.2 or 4.8 metres, precisely so that a run can be done in one piece without a joint. Buy long for those.

Common mistakes

• Assuming a stock length is exactly what it says — Timber is often cut slightly over-length, and end checks mean the first 50mm is frequently unusable. Do not design a cutting list that needs every millimetre of a stock length.
• Relying on a merchant's cut as a finished length — It is a transport cut, not a joinery cut. Squareness and length will both be approximate. Order oversize and trim at home.
• Buying three 2.4 metre lengths for a 3.4 metre run — A joint in the middle of a visible run looks like what it is. For skirting, architrave and shelving, buy the length that does it in one piece even if it costs more.

Questions people ask