| Nominal diameter | inch | Welded Pipe | SMLS Pipe(O.D.) | |
| DN6 | 1 /8 | 10 | ||
| DN8 | 2cents | 1/4 | 13.5 | 14 |
| DN10 | 3cents | 3 /8 | 17 | 18 |
| DN15 | 4cents | 1/2 | 21.25 | 22 |
| DN20 | 6cents | 3/4 | 26.75 | 25 |
| DN25 | 1inch | 1 | 33.5 | 32 |
| DN32 | 1inch2 | 1 1/4 | 42.25 | 42 |
| DN40 | 1inch5 | 1 1/2 | 48 | 48 |
| DN50 | 2inch | 2 | 60 | 57 |
| DN65 | 2inch5 | 2 1/2 | 75.5 | 74 |
| DN80 | 3inch | 3" | 88.5 | 89 |
| DN100 | 4inch | 4" | 114 | 108 |
| DN125 | 5inch | 5" | 140 | 133 |
| DN150 | 6inch | 6" | 165 | 159 |
| DN175 | 7inch | 7" | 194 | 194 |
| DN200 | 8inch | 8" | 219 | 219 |
| DN225 | 9inch | 9" | 245 | 245 |
| DN250 | 10inch | 10" | 273 | 273 |
| DN300 | 12inch | 12" | 325 | 325 |
| DN350 | 14inch | 14" | 377 | 377 |
| DN400 | 16inch | 16" | 426 | 426 |
| DN450 | 18inch | 18" | 478 | 478 |
| DN500 | 20inch | 20" | 529 | 529 |
| DN600 | 24inch | 24" | 630 | 630 |
| DN700 | 28inch | 28" | 720 | 720 |
| DN800 | 32inch | 32" | 820 | 820 |
- Generally speaking, the diameter of a pipe can be divided into outer diameter, inner diameter and nominal diameter.
1. The outer diameter of seamless steel pipe is represented by the letter D, followed by the outer diameter size and wall thickness. For example, a seamless steel pipe with an outer diameter of 108mm and a wall thickness of 5mm is represented by D108*5.
2. Galvanized steel pipes are represented by DN.
3. The nominal diameter must be used in the design drawings. The purpose is to determine the structural dimensions of pipes, pipe fittings, valves, flanges, gaskets, etc. based on the nominal diameter. The nominal dimensions are represented by DN. If the outer diameter is used in the design drawings, , a pipeline specification comparison table should also be made to indicate the nominal diameter and wall thickness of a certain pipeline.
- Although there are many standard systems applied in various countries around the world, they can be roughly divided into two categories, namely large outer diameter series and small outer diameter series. Large outer diameter series: (DN---nominal diameter.￠---outer diameter)
DN15---Φ22mm.
DN20---Φ27mm.
DN25---Φ34mm.
DN32---Φ42mm.
DN40---Φ48mm.
DN50---Φ60mm.
DN65---Φ76(73)mm.
DN80---Φ89mm.
DN100---Φ114mm.
DN125---Φ140mm.
DN150---Φ168mm.
DN200---Φ219mm.
DN250---Φ273mm.
DN300---Φ324mm.
DN350---Φ360mm.
DN400---Φ406mm.
DN450---Φ457mm.
DN500---Φ508mm.
DN600---Φ610mm.
Ø Small outer diameter series:
DN15---Φ18mm.
DN20---Φ25mm.
DN25---Φ32mm.
DN32---Φ38mm.
DN40---Φ45mm.
DN50---Φ￠57mm.
DN65---Φ73mm.
DN80---Φ89mm.
DN100---Φ108mm.
DN125---Φ133mm.
DN150---Φ159mm.
DN200---Φ219mm.
DN250---Φ273mm.
DN300---Φ325mm.
DN350---Φ377mm.
DN400---Φ426mm.
DN450---Φ480mm.
DN500---Φ530mm.
DN600---Φ630mm.
