Lumber size is often referred to as 4/4 (pronounced FOUR-QUARTER), 5/4 (FIVE-QUARTER), 6/4 (SIX-QUARTER) ETCETERA. This refers to the thickness of the lumber when it is first sawn, and in its rough size. The size increases in 1/4″ increments. 5/4 lumber measures one and one-quarter inches, or five 1/4″ increments. When surfaced, the lumber is dressed to 1″, and 4/4 would be dressed to 3/4″.