Lumber is wood that has been cut into boards or other shapes for the purpose of woodworking or construction. Lumber is supplied either rough or finished. Rough lumber is the raw material for furniture making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods. Finished lumber is supplied in standard sizes, mostly for the construction industry, and is primarily one of a few needle-bearing species such as hemlock, fir or spruce.
Rough lumber comes from the sawmill without further cutting or shaping. It is usually sold in random lengths and widths. It is available air-dried or kiln-dried. Air-dried lumber is carefully stacked and allowed to dry for several months, depending on thickness. It is used for some outdoor purposes, such as building sheds and fences. Kiln-dried wood is stacked in moisture and temperature controlled kilns built for the purpose and dried. It is then ready to be used for furniture-making or other woodworking uses.
Finished lumber is usually kiln-dried then planed and cut to predetermined sizes, primarily for use by the construction industry. These are nominal, rather than actual sizes. A 2x4 is actually 1-1/2 by 3-1/2 inches. Other stock is sized in similar way. The lengths are actual sizes and are multiples of 2 feet. Sizes from 8 to 16 feet are commonly available, and larger sizes are sometimes available.