Kreg Tool Tip: Understanding "Dimensional Lumber." Milled on all four sides and available in different lengths, "dimensional lumber" is used for a wide variety of wood projects and construction. Common woods like pine are sold as "dimensional lumber," with sizes listed as 1x4, 2x4, 2x6, and so on. These are the "nominal" dimensions of the boards—their size before final milling. The "actual" dimensions are smaller. For example, a 2x4 actually measures 1-1/2" x 3-1/2".