"dadiOH" wrote in :

Maybe 2x4s were once actually 2" x 4", don't know, best I remember is 1
5/8" x 3 5/8".

2x4 is the rough-sawn size. Our previous house was a 1928 farmhouse framed with rough-sawn
lumber: the wall studs were actually 2 inches by 4 inches, floor joists a full 2x8, etc.

The main advantage of dressing rough-sawn framing lumber is to provide consistent
dimensions: the actual size of the rough-sawn material varied +/- about 1/8".