- Nominal Size ("DN")
Nominal Size is a numerical designation of size that is common to all components in a piping system, other than components, designated by outside diameters or by thread size.
NOTE: The nominal size is designated by DN followed by a number. The nominal size cannot be measured, and should not be used for the purposes of calculation. It should be noted that not all piping components are designated by nominal size; for example, steel tubes are designated and ordered by outside diameter and thickness. It is a convenient round number for reference purposes and is loosely related to manufacturing dimensions.