The __________ size is the dimension of a piece of lumber before it is dried and surfaced.

The term that refers to the dimension of a piece of lumber before it is dried and surfaced is the nominal size. Nominal size is a traditional term that describes the dimensions of lumber as they are referred to in the industry, such as a 2x4, which means the wood is originally cut to those dimensions before undergoing the drying and surfacing processes.

When lumber is dried and surfaced, the dimensions become smaller due to the removal of moisture and the smoothing of the surfaces, which results in a smaller, actual size. Understanding the difference between nominal and actual sizes is essential for anyone working with lumber in construction, as it affects everything from material estimation to structural design.

Other terms such as finished and standard sizes also refer to specific uses and contexts within the lumber industry but do not accurately describe the dimensions prior to processing. Thus, the correct choice is nominal size, as it specifically denotes the size before any reduction due to drying and surfacing occurs.