In construction, there are lots of things that have nominal sizes that are not the actual size

For example, most houses are framed with sawn lumber called things like studs, joists and rafters.

A common piece of framing lumber used in a wall is called a stud.  One common size for a stud is a 2 by 4 usually written as 2 x 4.  But what size would a 2 x 4 actually measure?  Below is a chart that has the common sizes of framing members and their actual sizes in imperial measure, and in metric sizes.

Nominal Size Actual Size
1 x 2 3/4 x 1 1/2 inches (19 x 38 mm)
1 x 3 3/4 x 2 1/2 inches (19 x 64 mm)
1 x 4 3/4 x 3 1/2 inches (19 x 89 mm)
1 x 5 3/4 x 4 1/2 inches (19 x 114 mm)
1 x 6 3/4 x 5 1/2 inches (19 x 140 mm)
1 x 8 3/4 x 7 1/4 inches (19 x 184 mm)
1 x 10 3/4 x 9 1/4 inches (19 x 235 mm)
1 x 12 3/4 x 11 1/4 inches (19 x 286 mm)
2 x 2 1 1/2 x 1 1/2 inches (38 x 38 mm)
2 x 3 1 1/2 x 2 1/2 inches (38 x 64 mm)
2 x 4 1 1/2 x 3 1/2 inches (38 x 89 mm)
2 x 6 1 1/2 x 5 1/2 inches (38 x 140 mm)
2 x 8 1 1/2 x 7 1/4 inches (38 x 184 mm)
2 x 10 1 1/2 x 9 1/4 inches (38 x 235 mm)
2 x 12 1 1/2 x 11 1/4 inches (38 x 286 mm)
4 x 4 3 1/2 x 3 1/2 inches (89 x 89 mm)
4 x 6 3 1/2 x 5 1/2 inches (89 x 140 mm)
6 x 6 5 1/2 x 5 12 inches (140 x 140 mm)