Nominal Diameter (DN)/ Nominal Size (DN)

• Numerical designation of size which is a convenient round number approximately equal to the diameter in mm.

• The specified diameter, in millimetres, assigned to a nominal size.

NOTE: According to EN 1452, the nominal (outside) diameter of a thermoplastics pipe or a spigot, is equal to its minimum mean outside diameter, $d_{em,min}$

The nominal (inside) diameter of the socket of a fitting, pipe, valve or of ancillary equipment is equal to the nominal (outside) diameter of the connecting pipe for which they are designed.

• Numerical indication of size which is convenient integer approximately equal to the internal diameter (DN/ID) or the external diameter (DN/OD) in millimetres

• A numerical designation of the size of a component, other than a component designated by thread size, which is approximately equal to the manufacturing dimension, in millimetres (mm)

References

1. BS EN 12056-5:2000 Gravity drainage systems inside buildings
2. BS EN 1452-1:1999 Plastics piping systems for water supply- Unplasticized
3. BS EN 1253-1:2003 (Part 1)
4. BS EN 1329-1:1999