Flanges are an important component in piping systems, used to join pipes, valves, pumps, and other equipment. When selecting flanges, two main standards must be considered – DN (Dimension Nominal) and ANSI (American National Standards Institute). While both are common, there are some key differences to understand when choosing between DN vs ANSI flanges. This article will compare dn vs ansi flanges in detail to help you make the right choice.


Flanges provide a method to connect piping and transfer fluids or gases by bolting together with gaskets between them to seal the connection. They are used in many applications from the oil and gas industry to food and beverage processing, power plants, and more.

There are two main international standards for flange dimensions and ratings:

  • DN – Dimensional Nominal (European/ISO standard)
  • ANSI – American National Standards Institute (American standard)

While both follow the same design principle, there are variances in dimensions, pressure ratings, facings, and bolt patterns that make them non-interchangeable. Understanding dn vs ansi flanges will ensure you select the right flanges for your piping system.

Key Differences Between DN and ANSI Flanges

When evaluating dn vs ansi flanges, the following are the main factors to compare:


  • DN flanges are based on nominal pipe sizes with common diameter increments.
  • ANSI flanges have standard inch dimensions not directly related to pipe size.

This means DN 100 flange aligns with 100mm pipe, while ANSI 4” flange has a bore of approx. 4.5”. DN flanges use metrics while ANSI uses imperial units.

Pressure Ratings

  • DN flanges use PN rating – the maximum pressure in BAR at a given temperature.
  • ANSI flanges use Class rating – the maximum psi pressure based on material strength.

For example, a DN150 PN16 flange = ANSI 6” 150# flange in pressure handling capability.

Facing Styles

  • DN flanges use Form B1 or B2 facings.
  • ANSI flanges use Raised Face (RF) or Flat Face (FF) facings.

B1 is similar to RF, while B2 is comparable to FF. Facing must match for proper sealing.

Bolt Circles

  • DN bolt holes are located based on nominal diameter.
  • ANSI bolt circles are based on flange class rating.

Bolt holes will not align between the two styles.


  • DN flanges use metric based materials – P250GH, 1.4408, etc.
  • ANSI uses imperial/US grades – A105, A182 F316L, etc.

Material must be equivalent to handle required temperatures and pressures.

As you can see, dn vs ansi flanges have quite a few differences that make them non-interchangeable. Mixing the two often leads to leaks, damage, and other issues.

DN vs ANSI Flanges Size Chart

The Key Differences Between DN and ANSI Flanges

To compare common dn vs ansi flanges sizes, refer to this handy reference chart:

DN FlangeNominal Pipe SizeANSI Flange

This covers the most common dn vs ansi flanges sizes up to 16”. It gives an approximate comparison only – exact dimensions may vary. Confirm specifications before interchanging ANSI and DN flanges.

DN vs ANSI Flange FAQ

Some frequent questions about dn vs ansi flanges include:

Are DN and ANSI flanges interchangeable?

No, DN and ANSI flanges cannot be interchanged directly due to differences in dimensions, ratings, facings, and materials. Attempting to mate a DN flange to ANSI flange will result in misalignment.

Can you use a DN flange on ANSI pipe?

No, the differing dimensions mean a DN flange will not properly line up with ANSI pipe sizes. They are designed as systems to match DN flanges with DN piping, and ANSI with ANSI.

How do you convert DN to ANSI flange size?

There is no direct conversion between DN vs ANSI pipe sizes. The chart above provides an approximate equivalent for common DN and ANSI nominal flange sizes. Always check actual measurements – dimensions can vary across standards.

Should I use DN or ANSI flanges?

If your piping system is in locations using ISO standards (Europe, Middle East, Asia), DN flanges are likely required. For North America using ANSI standards, ANSI flanges will be the normal choice. Use the standard matching the rest of your piping for proper fit and function.

Can you bolt DN and ANSI flanges together?

You should never bolt together unmatched DN vs ANSI flanges. The different bolt circles will not align, resulting in improperly seated gaskets, leaks, and potential damage under pressure.


When it comes to selecting flanges, understanding the key differences between DN vs ANSI standards is critical. Mismatched flanges can lead to leakage, equipment damage, and costly repairs. By comparing dimensions, pressure ratings, facings, and materials, you can ensure you choose compatible DN or ANSI flanges every time.

With facilities across the globe, Jmet Corp provides both DN and ANSI flanges to meet local requirements. Contact us today to discuss your application and get help selecting the ideal flanges. Our experts can walk you through dn vs ansi flanges standards and provide reliable delivery on exactly what you need. Get the right flanges to keep your operations flowing smoothly.