For our example above, we are using a 4ply 2 X 12. 2" X 12" is the rough lumber dimension before it is run through the planer at the lumber mill. After it comes through the planer it will be 11/2" X 111/4" (so yes, a 2 X 12 does not measure 2" X 12"). This means that our 4ply 2 X 12 will be 4 X 11/2 inches wide or 6 inches. Therefore a post to support this builtup floor beam will need to ...