Answer by
Mable (3008)
Standardized lumber sizes are referred to as "nominal" and "actual" dimensions. "Nominal" is the size used to name the lumber -- in this case, 2 x 6. "Actual" refers to the measurements of the finished lumber. In this case, 2 x 6 lumber actually (or really) measures 2 1/2 x 5 1/2.