Denne tabellen viser sammenheng mellom National Pipe Size (NPS=Tommer) og DN (Diameter Nominal=mm).
| NPS (National Pipe Size) | DN (Diameter Nominal) |
| 1/8" | 6 mm |
| 3/16" | 7 mm |
| 1/4" | 8 mm |
| 3/8" | 10 mm |
| 1/2" | 15 mm |
| 5/8" | 18 mm |
| 3/4" | 20 mm |
| 1" | 25 mm |
| 1-1/4" | 32 mm |
| 1-1/2" | 40 mm |
| 2" | 50 mm |
| 2-1/2" | 65 mm |
| 3" | 80 mm |
| 3-1/2" | 90 mm |
| 4" | 100 mm |
| 4-1/2" | 115 mm |
| 5" | 125 mm |
| 6" | 150 mm |