A rough cut piece of lumber would actually measure around 1″ x 4″ and would be milled to a final thickness of 3/4″ x 3-1/2″.Click to see full answer. Also know, what is rough cut lumber?A saw that cuts lumber from a log is very large and aggressive, so the resulting lumber is known as “rough sawn” and the surfaces of the boards are . . . yes, rough and inconsistent. This lumber needs to be planed smooth and flat before being sized for the project at hand.Furthermore, is a 4×4 really 4 inches? Believe it or not, there actually is some rhyme and reason for why the actual measurements of dimensional lumber don’t match their names. Actual Dimensions and Nominal Dimensions. Nominal Measurement Actual (inches) Actual (mm) 2 x 12 1-1/2 x 11-1/4 38 x 286 4 x 4 3-1/2 x 3-1/2 89 x 89 4 x 6 3-1/2 x 5-1/2 89 x 140 Then, how do you measure rough lumber? Let’s Size Some Wood: Rough crosscut your rough lumber. Joint and straighten one edge. Rip the rough width 1/4″ wider than the finished width. Joint one face of the board flat. Plane the board to its finished thickness. Joint one edge square. Rip to the finished width plus 1/32″. What is full dimension lumber?All lumber gets cut to the specified dimensions, but almost all methods of drying and processing will shrink the boards to some degree. This is why it is called full-dimensional lumber. An air-dried two-by-four still measures very close to two inches by four inches.