DN, PN and Schedule: Pipe Reference Figures Explained Simply

Anyone ordering pipes and flanges soon comes across abbreviations such as DN, PN and Schedule. These reference figures describe size and pressure capacity and ensure that components fit together. We explain them clearly.

DN – the nominal diameter

DN (Diameter Nominal) denotes the standardised nominal diameter of a pipe or component, for example DN 50 or DN 100. It is a dimensionless parameter and corresponds approximately, but not exactly, to the inside diameter in millimetres. The actual outside diameter is standardised: DN 50 corresponds to 60.3 mm, DN 100 corresponds to an outside diameter of 114.3 mm.

PN – the pressure rating

PN (Pressure Nominal) specifies the standardised pressure rating, i.e. the permissible pressure at reference temperature in bar. Common ratings are PN 6, PN 10, PN 16, PN 25, PN 40 and higher. Flanges, valves and pipes of one PN rating fit together. As the temperature rises, the permissible operating pressure decreases – the exact values are provided by the pressure-temperature tables of the standard.

Schedule – the wall thickness

The Schedule (Sch. or S) originates from the Anglo-American world (ASME B36.10/B36.19) and describes the wall thickness of a pipe at a given outside diameter. Sch. 10, 40 and 80 are common: the higher the number, the thicker the wall and the greater the pressure capacity. In Europe, the wall thickness is often given directly in millimetres.

How it all fits together

For a leak-tight, pressure-resistant connection, the nominal diameter (DN), pressure rating (PN) and sealing face must match. For enquiries, DN, PN, material and quantity are all we need – we assemble matching pipes, bends, flanges and gaskets.

Frequently Asked Questions

What does DN mean for pipes?

DN (Diameter Nominal) is the standardised nominal diameter. It is dimensionless and corresponds approximately to the inside diameter; the outside diameter is fixed by standard, e.g. DN 100 = 114.3 mm.

What is the difference between PN and Schedule?

PN describes the pressure rating (permissible pressure in bar at reference temperature), while Schedule describes the wall thickness of a pipe at a given outside diameter to ASME. Both relate to pressure capacity.

Does the permissible pressure fall as temperature rises?

Yes. The PN rating applies at reference temperature. As the operating temperature rises, the permissible pressure decreases; the exact values are given in the pressure-temperature tables of the relevant standard.