Understanding Dimensions 69
ample, a finished (dressed) 2 x 4 piece is less than 2 inches thick and less than 4 inches wide. The nom-
inal size is usually greater than the actual dimension.
When sawn lumber (nominal size) is seasoned, dressed, or planed, the size becomes smaller; this
is the “actual size.” For example, a piece of 2 x 4 lumber (100 x 50) may become approx 11/2 x 31/2
inches (90 x 45) when it has been dressed or planed. The actual size therefore refers to the minimum
acceptable size after it has been dressed and seasoned. A nominal 2 x 4 can have a minimum actual
size of 1.5 x 3.5 inches. When referring to a specific piece of lumber, the nominal size is used. Figure
4.11 shows examples of nominal and actual sizes of lumber and boards.
Figure 4.10 A drawing showing the use of reference dimensions.