What Is the Difference Between ANSI and DIN Flanges?

When sourcing flanges for global projects, one of the first decisions you’ll run into is choosing between ANSI and DIN standards.

While they serve the same purpose—connecting pipes and equipment—these standards are built around different engineering systems.

Different Standards, Different Foundations

ANSI and DIN flanges follow two distinct engineering systems—each with its own approach to sizing and pressure ratings.

ANSI (American National Standards Institute) uses imperial units—like inches for size and pounds per square inch (psi) for pressure. It’s primarily followed in the U.S., Canada, and parts of Latin America. ANSI flanges are typically designed in line with ASME B16.5 or B16.47 standards for steel piping.
DIN (Deutsches Institut für Normung) uses the metric system—millimeters for diameter and bar for pressure. These flanges are commonly used across Europe, Asia, and many other regions that follow international metric engineering standards.

Because the two systems are built on different fundamentals, they’re not interchangeable—even if two flanges appear to have the same nominal size.

Dimensional and Design Differences

At a glance, an ANSI flange and a DIN flange might look similar, but the details tell a different story:

Bolt hole layouts
DIN and ANSI flanges differ in both bolt circle dimensions and the number of bolt holes. For example, a DIN PN16 DN100 flange typically uses 8 holes, but its ANSI Class 150 equivalent might use the same number or even fewer—depending on the exact standard.
Thickness and face design
ANSI flanges tend to be thicker, especially in higher pressure classes, and often have raised faces. DIN flanges can have flat face or raised face types, but the thickness is determined by PN class. These differences impact not only sealing but also torque values and gasket choices.
Pressure ratings
ANSI flanges are categorized by pressure classes—Class 150, 300, 600, etc.—measured in psi. DIN flanges use the PN rating system (e.g., PN10, PN16), which represents bar pressure at 20°C. These systems don’t convert directly, so a PN16 DIN flange isn’t a one-to-one match with a Class 150 ANSI flange.

Why They’re Not Interchangeable

Even if an ANSI and DIN flange are labeled for similar pressure or pipe size, they aren’t compatible without an adapter. That’s because the differences in bolt holes, flange thickness, and face types prevent a proper seal. Attempting to mix them without proper conversion introduces risk—either in performance failure or safety.

If a project spans multiple standards—say, European-supplied equipment in a U.S.-based facility—it’s critical to use proper adapters designed to transition between DIN and ANSI systems. These must also match pressure and temperature requirements to avoid system failure.