When employing 2-by-4 studs and half-inch drywall, the standard internal wall thickness in contemporary construction is 4.5 inches. Plumbing-containing walls often have 2-by-6 studs, which results in 6.5-inch walls. Depending on the outside treatment, siding, and brick facing, exterior wall thickness varies.
The size of green, rough-sawn studs is the nominal dimension of 2-by-4 (inches). The finished size is reduced to the present standard of 1.5 by 3.5 inches by drying and planing. In ancient buildings, the interior walls may be different.
Prior to 1970, studs were 3 5/8 inches thick rather than 3.5 inches, and lath and plaster is slightly thicker than half-inch drywall. Even earlier, 2-by-4s that had been rough-sawn in the green were brought and planed on site to a completed size according to a standard set only by the specific carpenter.
The width of the door frame should be measured, and the thickness of the trim should be subtracted to get the wall thickness in an existing home.