Diameters in DN or in NPS
From within the industrial market we find these two systems to size the diameters for pipes, tubes, valve connections and other devices:
- Nominal pipe size (NPS) , defined by the American standard ANSI / ASME is based on inches .
- Nominal diameter (DN) , defined by the European standard ISO 6708 is based on millimeters .
We know that to determine the conversion operation from one value to another, we should only perform a simple simple mathematical formula (the value of a inch is 25.4 millimeters and that of 1 millimeter 0.0393701 inches); however we could not apply it to determine these values because each system uses a commercial measure that does not correspond with the real value of the outside diameter of the pipe but with the inside of it. We observe a difference of 0.4 millimeters in the value DN 25 while in larger sizes the difference is even greater , for example: 120 inches is actually 3048 millimeters, 48 millimeters more than the DN 3000 value.
In order to make things easier for you, you have below a conversion table so that you can determine the equivalent value of each measure .
| DN (Diameter Nominal) Milimeters | NPS (Nominal Pipe Size) Inches |
| 6 | 1/8 |
| 8 | 1/4 |
| 10 | 3/8 |
| 15 | 1/2 |
| 20 | 3/4 |
| 25 | 1 |
| 32 | 1 1/4 |
| 40 | 1 1/2 |
| 50 | 2 |
| 65 | 2 1/2 |
| 80 | 3 |
| 90 | 3 1/2 |
| 100 | 4 |
| 115 | 4 1/2 |
| 125 | 5 |
| 150 | 6 |
| 200 | 8 |
| 250 | 10 |
| 300 | 12 |
| 350 | 14 |
| 400 | 16 |
| 450 | 18 |
| 500 | 20 |
| 600 | 24 |
| 700 | 29 |
| 800 | 32 |
| 900 | 36 |
| 1000 | 40 |
| 1050 | 42 |
| 1100 | 44 |
| 1200 | 48 |
| 1300 | 52 |
| 1400 | 56 |
| 1500 | 60 |
| 1600 | 64 |
| 1700 | 68 |
| 1800 | 72 |
| 1900 | 76 |
| 2000 | 80 |
| 2200 | 88 |
| 2400 | 96 |
| 2600 | 104 |
| 2800 | 112 |
| 3000 | 120 |
| 3200 | 128 |
| 3400 | 134 |
| 3600 | 142 |
| 3800 | 150 |
