DN Pipe Size Table (with NPS Conversion) — What You Must Know Before Choosing a Valve

When installing or purchasing valves, many people often encounter terms like "DN", "NPS", "OD" (Outer Diameter), "Wall Thickness", etc. These can be confusing—especially when you're coordinating projects or ordering valves and fittings. If you don’t understand these terms clearly, you risk mismatches, wasted time, or even installation failures.

This article explains DN (Nominal Diameter), NPS (Nominal Pipe Size), how to convert between them, how to read pipe size tables, and how to choose the correct valve—all in simple and practical language.

1. What Does DN Mean?

DN stands for "Nominal Diameter", a standardized way to identify the size of a pipe or valve.

• It does not represent the exact inner or outer diameter.

• DN is expressed in millimeters (mm). Common sizes include: DN15, DN20, DN25, DN50, DN100, etc.

Example: A DN50 pipe has an actual outer diameter of 60.3 mm. The “50” is just a nominal label for classification.

2. What Is NPS? How Is It Different from DN?

NPS stands for "Nominal Pipe Size", commonly used in the U.S., Canada, and other countries using the imperial system.

• It’s expressed in inches (e.g., NPS 2, NPS 4).

• Like DN, NPS is also a nominal number and does not reflect exact dimensions.

DN and NPS Conversion Table (Common Sizes)

✅ Tip: Although DN and NPS come from different systems, they are often used together and can be matched one-to-one.

3. Don’t Forget Wall Thickness (Schedule)

Even if two pipes are the same DN or NPS, they may have different wall thicknesses, which affects pressure tolerance.

• Wall thickness is expressed in "Schedule" (Sch) — like Sch10, Sch40, Sch80.

• For example, DN50 (NPS 2) pipe:

• Sch 40: ~3.91 mm wall thickness

• Sch 80: ~5.54 mm wall thickness

➡️ When selecting a valve, especially for welded connections, wall thickness must match for proper fit and sealing.

4. What You MUST Know Before Choosing the Right Valve

1. What’s the pipe’s nominal diameter (DN or NPS)?
   → If your pipe is DN80, choose a valve with DN80 connection.

2. What type of connection is used?

• Flanged (most common)

• Threaded (for small pipes)

• Welded (for high-pressure applications)

3. What is the wall thickness (Schedule)?

• Especially important for welded valves and pipes.

4. What pressure rating is required?

• For example, PN16, PN25, etc. (PN stands for pressure nominal in bar)

5. Why Does This Matter So Much?

• Correct installation: Matching the right valve to the pipe prevents delays and rework.

• Cost-saving: Choosing the right product avoids waste and extra logistics.

• Smooth international projects: Especially critical in mixed metric/imperial systems.

6. What Can We Offer?

As a professional valve manufacturer, we provide:

✅ Full range of DN standard valves
✅ Support for both metric and imperial systems
✅ Detailed technical drawings, size charts, and consultation
✅ Valve types: Ball valves, Butterfly valves, Gate valves, Check valves, Pneumatic/Electric valves, and more
✅ Factory-direct supply, fast delivery, reliable quality

Conclusion

Whether you're an engineer or a buyer, understanding DN/NPS and pipe dimensions is essential for successful valve selection and project execution.

We hope this article helped you:

• Understand DN, NPS, OD, and wall thickness

• Learn how to use a pipe size conversion table

• Confidently choose the right valve

Want the complete DN/NPS Pipe Dimension Chart (PDF) or a free valve selection consultation? Contact our technical team — we’re happy to help!