If you’re looking to build a deck for the very first time, the first thing you need to know is how much decking to buy. Many people make the mistake of planning their materials list based on what’s known in the lumber world as “nominal dimensions.” 1×4, 1×6, 5/4×4, and 5/4×6. These are the most popular “nominal dimensions” and are the terms we are all used to hearing on TV shows and even in DIY deck building books. However, what you need to know is that “nominal dimensions” refer to a piece of unfinished/rough lumber that has not yet been milled (aka surfaced).