Dimensional lumber is cut to a specific length, width, and depth. However, there is a difference between the nominal size (what the lumber is referred to) and the actual size. The tables below provide both the nominal and actual lumber dimensions for many common North American lumber sizes....
When we talk about Nominal vs Actual, we are referring to the size of materials. This is particularly relevant to structure, such as the timer/lumber sizes. In North America one of the most common lumber sizes is 2×4. So, you would think that when you draw a wall with 2×4, that ...
The size of pipes, fittings, flanges and valves are often given in inches as NPS - Nominal Pipe Size, or in metric units as DN - 'Diametre Nominal'.
It is just a convenient and easy way to identify pipe and lumber. Outside diameter (OD) and inside diameter (ID), as their names imply, categorize pipes by their true outside and inside measurements. One of the complexities of pipe design is that different sizes of pipe are manufactured ...