GB/T 1047-2005 "Pipeline Components DN (Definition and Selection of Nominal Dimensions)" is defined as follows:
A nominal size is an alphanumeric dimensional designation used for piping system components, consisting of the letters DN followed by a dimensionless integer number. This number is directly related to characteristic dimensions such as the bore diameter or outer diameter (expressed in mm) of the end connection.
The nominal size DN is a convenient rounded number for reference purposes. Unless otherwise specified, the number after DN does not represent a measurement and is not used for calculation purposes. Other technical standards that use the DN designation should give the relationship between the DN and the size of the pipe element, such as DN/OD or DN/ID.
1in=25.4mm
1 wire=0.01mm
