What Do DN and PN Mean on Flanges?

If you’ve ever looked at a flange label and wondered what DN and PN actually stand for, you’re not alone. These markings are standard in metric piping systems, but they’re easy to overlook until you’re matching parts or building to spec. 

Here’s a quick breakdown to help you get it right—whether you’re designing a system or reviewing a supplier’s datasheet.

What Does DN Mean?

DN stands for Diameter Nominal. It’s a metric-based sizing system that gives you a standard way to refer to pipe and flange diameters—without getting into the exact inner or outer dimensions. For example, DN50 generally refers to a pipe with a 50mm nominal bore, even though the actual measurement may vary depending on wall thickness or schedule.

The goal of DN sizing is consistency across global systems. Whether you’re ordering fittings, valves, or flanges, a DN-marked flange tells you it will fit the matching pipe, no matter the material or manufacturer. It’s especially useful when working across suppliers or coordinating between design and procurement teams.

What Does PN Mean?

PN means Pressure Nominal, and it shows the bar-rated pressure a flange is designed to withstand at 20°C. So, a PN16 flange is rated for 16 bar of pressure (around 232 psi). It’s not just a pressure cap—PN ratings help define the flange’s wall thickness, bolt pattern, and material strength.

You’ll see PN ratings like PN6, PN10, PN16, and higher. Choosing the right one depends on your system’s working pressure and temperature range. If you’re dealing with high-temp or fluctuating loads, you may need a higher PN to maintain safe operation under stress.

Why DN and PN Matter Together

When sourcing flanges, DN and PN must work together. 

The DN tells you if it fits your pipe. The PN tells you if it can handle your system’s pressure. Mismatching the two—like using a PN6 flange in a 20-bar system—can result in a failure risk, even if the dimensions technically match.

You’ll often see both marked right on the flange (e.g., “DN100 PN16”), along with the material grade and standard (like EN 1092-1). That’s your signal that the flange meets both size and pressure expectations.

Sourcing the Right Flange

For critical systems, especially in industrial, water, or chemical processing environments, it’s not enough to go by size alone. You’ll want to:

• Confirm the DN matches your pipe bore
• Select a PN value that’s higher than your system’s maximum working pressure.
• Choose a PN rating that exceeds your system’s peak operating pressure.
• Make sure the flange meets applicable standards such as EN, ISO, or ASME.

What Do DN and PN Mean on Flanges: Final Take

What do DN and PN mean on flanges? DN gives you the size; PN gives you the pressure rating. Together, they help ensure you’re specifying flanges that fit your system and hold up under operating conditions.

Need help selecting the right flange for your setup?

Longan Flange offers a full range of stainless steel and ASME-compliant flanges with clear DN and PN labeling—built to match your specs and simplify installation.