What is the dimension of a standard 2"x4" piece of lumber after it is surfaced?

The standard dimensions of a 2"x4" piece of lumber refer to its nominal size, which is often different from its actual dimensions after processing. When lumber is milled, it is planed and surfaced to create a smooth finish, resulting in a reduction of size.

For a nominal 2"x4", the actual dimensions after surfacing typically measure 1-1/2 inches in thickness and 3-1/2 inches in width. This makes option B correct, as it accurately reflects the actual dimensions of a surfaced 2"x4".

This variance in size is due to the lumber drying and shrinking during the milling process, as well as the removal of rough edges and surfaces. The production of lumber follows specific industry standards which define these nominal vs. actual sizing conventions.