CONVERSION TABLE DN TO INCH
| 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 |
| DN (Diameter Nominal) Milimeters | NPS (Nominal Pipe Size) Inches |
| 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 |
| DN (Diameter Nominal) Milimeters | NPS (Nominal Pipe Size) Inches |
| 700 | 28 |
| 800 | 32 |
| 900 | 36 |
| 1000 | 40 |
| 1050 | 42 |
| 1100 | 44 |
| 1200 | 48 |
| 1300 | 52 |
| 1400 | 56 |
| 1500 | 60 |
| 1600 | 64 |
| 1700 | 68 |
| DN (Diameter Nominal) Milimeters | NPS (Nominal Pipe Size) Inches |
| 1800 | 72 |
| 1900 | 76 |
| 2000 | 80 |
| 2200 | 88 |
| 2400 | 96 |
| 2600 | 104 |
| 2800 | 112 |
| 3000 | 120 |
| 3200 | 128 |
| 3400 | 134 |
| 3600 | 142 |
| 3800 | 150 |
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 above a conversion table so that you can determine the equivalent value of each measure .
Bolts diameter to Inch
M 6 = inch
M 8 – inch
Hello
Your conversion table is practical and useful
Thank you
Thank you! We use it a lot ourselves!
VERY NICE . THANKS
Does this mean that I can thread a DN15 male into a 1/2″ female, for example?
Short answer: Not necessarily. DN15 only defines the nominal bore (~15 mm). It does not define the thread form. You can only mate a DN15 male with a 1/2″ female if both use the same thread standard and sealing method.
Details:
DN ↔ inch is only a nominal size equivalence (DN15 ≈ 1/2″).
It says nothing about thread type (BSPP, BSPT, NPT, metric), taper, thread angle, or sealing principle.
Common DN15 thread options:
G 1/2 (BSPP, parallel) – 55° profile, parallel thread; seals with gasket/O-ring/flat face.
R 1/2 (BSPT, tapered) – 55° profile, tapered male; seals on the threads with sealant.
1/2″ NPT (tapered) – 60° profile, tapered; seals on the threads with sealant.
Mixing standards is not recommended:
A BSP and an NPT thread may appear to engage and you can often screw them together partially, but due to the different thread angle (55° vs 60°) and taper geometry, they will not fully seat, won’t seal correctly, and may damage the threads.
This often leads to leaks or even mechanical failure under pressure.
Rule of thumb:
DN15 ≈ 1/2″ for the nominal diameter, but you must always check the thread standard.
Only mate BSP with BSP and NPT with NPT (or use the proper certified adapter).
Very helpful, Pol, thank you!
pls make a chart for valve thickness according to of OD, NPS and RATING
Good question, and honestly a very interesting topic.
We don’t have a standard chart published for that at the moment, since valve body thickness depends on several factors like design, material and applicable codes (e.g. ASME B16.34), not only OD, NPS and rating.
That said, we’ll definitely take note of it as a potential topic for a future blog post — it’s the kind of practical content that can be really useful in real projects.
If you have a specific case in mind, feel free to share it and we can take a closer look.