In modern construction, the traditional lumber sizes are two-bys (2x4s, 2x6s, 2x10s, etc.), which detail a board’s thickness in inches. These are the basic building blocks for residential construction.
Every piece of lumber has a nominal dimension and a finished dimension, as the nominal dimension depicts the size of the green (not dried), rough (unfinished) piece of lumber.
Find more information below on lumber sizes for residential projects.
National Institute of Standards and Technology: American Softwood Lumber Standard