Understanding Wood Sizes

Timber merchants sell most of their wood in standard pre-cut sizes. The stan¬dard lengths for softwoods start at 1.8m and increase in multiples of 0.3m to a length of 3.9m, though both longer and shorter lengths can be obtained. With hardwoods the situation is much more complicated and as it is likely that a timber merchant will stock relatively few sizes, it is worth checking with him before deciding on what lengths to buy. In very general terms, hardwoods start at 1.8m in length, though shorter lengths are often available.

The standard widths and thicknesses available depend on whether the timber is left rough sawn or planed smooth.

For softwood, two finishes are widely available:

Sawn
The timber is cut to standard sizes in both width and thickness by large power saws. Sawn timber is sold by its nominal size - as cut from the log. After drying, timber shrinks slightly so the size of sawn timber when it is bought is slightly less than its nominal size.

Planed all round (PAR)
This is sawn timber which has had all its sides smoothed and made parallel by planing. A PAR size is usually around 3 to 5mm less than the nominal sawn size.

The sizes of timber available are based on the metric equivalents of the original inch sizes. Many timber merchants still talk and think in inches, and you may even find nominal sizes quoted in inches with finished sizes in millimetres!

The most common thicknesses for both sawn and planed softwood timber start at 12mm (1/2 in) and go up to 100mm (4in). Intermediate sizes are 19mm, 25mm, 32mm, 38mm, 50mm, 63mm and 75mm, though you may also find 16mm and 22mm thicknesses for planed timber.

The common widths start at 25mm (lin) and go up in 25mm steps to 225mm with just one fairly common intermediate size (38mm) and a few less common ones (32mm, 112mm and 138mm, for example).

Not all thicknesses are available in all widths, and some sizes are available only as planed timber or only as sawn timber. Small sizes are generally available as mouldings.

Where wood needs to be a specific size (for joists or studs, for example) you can get regularised timber which is exactly its stated size.

For most do-it-yourself work, you will be using a limited range of sizes - typi¬cally 25mm by 50mm, 25mm by 100mm and 25mm by 150mm planed softwood and 50mm by 100mm or 50mm by 200mm sawn softwood and these should be readily available.

The sizes of pine available for shelving generally stops at 225mm (9in); for wider sizes you will have to go to parana pine.

Hardwood is always sold as planed all round and the number of sizes available is likely to be more restricted: ramin comes in smaller sizes than red hardwood.
You might also want to learn how to diagnosis floor problems and how to fill cracks in brickwork and concrete because you would encounter these issues while working with wood in your house.