Farmhouse-Trim-Measurements A – 31.5″ B – 63″ The top trim is a combination of a essentially three pieces, a larger top molding, a flat board and then a smaller bottom molding. The area marked “C” is the setback of what was originally the drywall and our contractor stacked it out where that piece met the front facing piece. C – 4.25″ D – 3.5″ E – 1″ F – 4.5″ G – 2.25″
The way you can do it is the - by half measure - eg. 8 ft.wall = 4 inch base or 12 ft. wall = 6 inch base and so on . You don't have to be exact because baseboards are not exact sometimes . So your 4 1/2 inch base will work for a 9 ft. wall height . for trims around doors etc. I just do 3 to 4 inches.