What is DN in Pipes?

  1. “DN” is an abbreviated form of Diameter Nominal (DN).
  2. It is a dimensionless number that denotes the pipe size in the metric unit system.
  3. The DN pipe size designator is developed by the International Standards Organization or ISO.
  4. The pipe sizes are designated by DN followed by a number to indicate standard pipe size. For example, DN50 indicates a 2″ NPS pipe; Similarly, DN80 indicates a 3″ NPS pipe.

What is PN in Pipes?

  1. NPS or Nominal pipe size is also a dimensionless pipe size designator.
  2. A specific pipe size is indicated by NPS followed by a number. For example, NPS 2 indicates a pipe having an outside diameter of 2.375 inches.
  3. The pipe outside diameter is more than its NPS designator for NPS 12 and smaller pipes. However, NPS 14 and larger pipes have the same pipe OD in inches as the NPS designator. This means an NPS 24 pipe has an OD of 24 inches.


  • So, the main difference between DN and NPS is that DN indicates the approximate pipe dimensions in mm whereas the NPS indicates the pipe dimension in inches.
  • For pipes larger than NPS 3.5, the DN number is calculated by multiplying the NPS size designation number by 25. For example, NPS 4 is the same as DN 100.

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