Understanding the lumber nominal size chart is essential for anyone involved in construction, woodworking, or home improvement. The numbers stamped on a board, such as 2x4 or 1x6, rarely match its actual dimensions, creating confusion for beginners and even experienced professionals. This discrepancy between the name and the reality is a standardized practice rooted in historical manufacturing processes.
The Reason Behind Nominal Sizing
The primary reason for the difference between nominal and actual size lies in the milling and drying processes. When a tree is first cut, the wood is green and wet, containing a high moisture content. The nominal dimensions, like two inches by four inches, reflect the rough-sawn size of the board directly from the mill before it is dried and planed.
Drying and Surfacing
As the wood dries, it naturally shrinks. Following this, the board is run through a planer, which smooths and flattens the surface by removing a thin layer of material. This process of surfacing both reduces the thickness and width of the board significantly. Consequently, a board labeled as 2x4 will typically measure 1.5 inches by 3.5 inches after it has been dried and finished.
Common Dimensional Lumber Sizes
The standard dimensional lumber found in North America follows a predictable pattern. Framing members used for walls and roofs are most commonly available in specific sizes that adhere to this standard. The actual dimensions are always slightly smaller than the name, which is important to remember when calculating material quantities or designing joinery.
