Lumber Nominal Sizes

When somebody talks about a 2×4 board, do you assume it’s actually 2 inches by 4 inches? A reasonable assumption, until you try to build something based on those dimensions. The “2×4” label is what’s known as the “Nominal Dimension”, and is the size a board originally was before it was trimmed and cleaned up for sale. After being trimmed, the “Actual Dimension” of that board is smaller. Instead of having to memorize the actual sizes, here’s a handy chart of some common sizes. Note that these do not apply to sheet goods like plywood. If that says it’s a 1/4″ thickness or 1/2″ thickness, it may not be PERFECT but its pretty close.