Standards guide · Flanges
EN 1092-1 vs ASME B16.5: flange standards compared
EN 1092-1 (Europe) and ASME B16.5 (USA) describe the same component with different systems: DN versus NPS, PN versus Class, form B1 versus raised face. This page sets the terms side by side, compares the dimensions of common sizes (PN 16 vs Class 150) – and explains why “roughly matching” flanges must never be bolted together.
- Europe
- EN 1092-1
- USA
- ASME B16.5
- Designators
- DN · PN vs. NPS · Class
- Interchangeable?
- No – adapter required
Two standards worlds, one component
EN 1092-1 (Europe) and ASME B16.5 (USA) describe the same component with different systems. The central pairs of terms:
Nominal size
DN vs NPS
The European nominal size DN is a dimensionless metric designator; the American nominal pipe size NPS counts in inches. DN 50 ↔ NPS 2 belong to the same pipe (60.3 mm outside diameter) – the pipe outside diameters of the two worlds are largely identical, because both build on the same historical inch dimensions. Two exceptions: DN 65 with 76.1 mm (EN) versus 73.0 mm (2 1/2″, ASME) and DN 125 with 139.7 mm versus 141.3 mm (5″).
Pressure rating
PN vs Class
PN (“nominal pressure”) is a reference designation that the bar figures at room temperature lean on – but PN 16 does not simply mean 16 bar: the actually permissible pressure depends on material, temperature, flange type and the applicable code, among other factors. The ASME Class (150, 300, 600 …, also written “lbs” or “#”) is likewise a dimensionless designator: Class 150 does not mean 150 psi – the permissible pressure depends on material and temperature and is given in the pressure-temperature tables of the standard.
Common to both: the permissible pressure drops as temperature rises; interpolation is permitted for intermediate temperatures. The individual ASME styles (weld neck, slip-on, lap joint …) and their EN type numbers are explained on the page Flange types international.
Matching nominal sizes and pressure ratings
PN ↔ Class: the translation table and its limits
The industry-typical rough matching of the pressure ratings:
| PN (EN 1092-1) | Class (ASME B16.5) |
|---|---|
| PN 16 | Class 150 |
| PN 40 | Class 300 |
| PN 100 | Class 600 |
| PN 160 | Class 900 |
| PN 250 | Class 1500 |
| PN 400 | Class 2500 |
Important: this is a purchasing orientation, not technical equality. Bolt circles, numbers of holes, bolt sizes and overall dimensions differ – a Class 150 flange does not mechanically fit a PN 16 counterflange, even though both can take “roughly the same pressure”. There is no exact 1:1 translation, only functional equivalence per application – the bolt circles alone already differ.
DN ↔ NPS: matching the nominal sizes
No exact 1:1 translation: the DN ↔ NPS matching only names which nominal sizes belong to the same pipe. The flange dimensions (bolt circle, number of holes, outside diameter, bolts) are not interchangeable – same pipe, incompatible connection.
| DN | NPS |
|---|---|
| 15 | 1/2" |
| 20 | 3/4" |
| 25 | 1" |
| 32 | 1 1/4" |
| 40 | 1 1/2" |
| 50 | 2" |
| 65 | 2 1/2" |
| 80 | 3" |
| – 1 | 3 1/2" |
| 100 | 4" |
| 125 | 5" |
| 150 | 6" |
| 175 | – 2 |
| 200 | 8" |
| 250 | 10" |
| 300 | 12" |
| 350 | 14" |
| 400 | 16" |
| 450 | 18" |
| 500 | 20" |
| 550 | 22" 3 |
| 600 | 24" |
1 For
NPS 3 1/2" our
PN dimension tables (PN 6 – PN 40)
list no matching DN size – pipes and fittings in this size
(outside diameter 101.6 mm) do exist nonetheless.
2 DN 175 (pipe outside diameter 193.7 mm) is
in use as a pipe nominal size but has no flange counterpart in
ASME B16.5.
3 22" (DN 550) is not standardised in ASME B16.5 but is common in the trade as a manufacturer standard (cf. MSS SP-44) – for connection dimensions see our ASME dimension tables; agree the bolt-hole pattern explicitly when ordering.
Dimensional comparison of common sizes: why the dimensions do not match
Both standards build on the same pipe outside diameters, but flange outside diameter, bolt circle, number of holes and flange thickness are defined independently. Example: DN 100/PN 16 has 8 bolts (holes 8 × 18 mm) on a 180 mm bolt circle; NPS 4/Class 150 has 8 bolts (holes 8 × 19.1 mm) on a 190.5 mm bolt circle – looks similar, does not fit. Rule of thumb: same pipe, incompatible connection. The pipe itself can certainly be combined across the worlds – an ASME pipe can be worked with an EN flange, except for the deviating outside diameters 76.1/73.0 mm and 139.7/141.3 mm; what is incompatible is the flange connection.
On narrow screens the table scrolls sideways.
| Pairing | Standard · rating | Holes n × Ø (mm) | Sealing face (mm) | Bolt circle (mm) | Outside Ø (mm) |
|---|---|---|---|---|---|
| DN 25 ↔ 1" | DN 25 · PN 16 | 4 × 14 | 68 | 85 | 115 |
| 1" · Class 150 | 4 × 15.7 | 50.8 | 79.2 | 108 | |
| DN 50 ↔ 2" | DN 50 · PN 16 | 4 × 18 | 102 | 125 | 165 |
| 2" · Class 150 | 4 × 19.1 | 91.9 | 120.7 | 150.4 | |
| DN 80 ↔ 3" | DN 80 · PN 16 | 8 × 18 | 138 | 160 | 200 |
| 3" · Class 150 | 4 × 19.1 | 127 | 152.4 | 190.5 | |
| DN 100 ↔ 4" | DN 100 · PN 16 | 8 × 18 | 158 | 180 | 220 |
| 4" · Class 150 | 8 × 19.1 | 157.2 | 190.5 | 228.6 | |
| DN 150 ↔ 6" | DN 150 · PN 16 | 8 × 22 | 212 | 240 | 285 |
| 6" · Class 150 | 8 × 22.4 | 215.9 | 241.3 | 279.4 | |
| DN 200 ↔ 8" | DN 200 · PN 16 | 12 × 22 | 268 | 295 | 340 |
| 8" · Class 150 | 8 × 22.4 | 269.7 | 298.5 | 342.9 |
The complete dimension tables of all sizes and pressure ratings are on the two detail pages: flange dimensions PN 6 – PN 40 to EN 1092-1 and – currently in German – flange dimensions to ASME B16.5 (Class 150/300/600); an English version of the ASME tables will follow.
Facings: form B1 meets raised face
- EN 1092-1 defines the facing forms A–H (including form A flat, forms B1/B2 with raised sealing face and defined roughness, tongue/groove C/D, male/female E/F, O-ring forms G/H) – for details see our flange guide.
- ASME B16.5 knows the facing forms flat face (FF), raised face (RF, standard), ring type joint (RTJ), tongue & groove and male & female. The lap-joint flange, by contrast, is a flange style, not a facing type – there the sealing face sits on the stub end. RF is the default – anyone needing FF or RTJ has to order it explicitly.
- RF height to ASME: Class 150/300 → 1.6 mm; from Class 400 → 6.4 mm. In the EN world the height of the raised face is included in the form B dimension tables – a frequent stumbling block when comparing overall dimensions.
- Surface finish (“face finish”, ASME environment): stock finish (standard spiral groove, Ra approx. 3.2–12.5 µm), spiral/concentric serrated, smooth finish for soft gaskets – the roughness must suit the gasket (PTFE/soft → smoother, spiral-wound → standard).
- Pairing rule (ASME B31.3): never bolt FF against RF – risk of leakage and fracture (cast materials).
- Functionally, EN form B1 and ASME RF with stock finish are the closest match; they are not identical (check roughness).
Conclusion: when directly compatible, when an adapter?
- Same standards world on both sides of the joint → no problem: only flanges of the same standard, nominal size and pressure rating fit together.
- EN plant meets US equipment (or vice versa) → design the transition deliberately: procure a matching counterflange to the other standard or use an adapter solution (transition piece with a matching connection on each side, special flange to drawing).
- Never bolt “roughly matching” flanges together – even if the number of holes is the same, bolt circle and bolt size do not match.
Zickwolff supplies both standards worlds, checks parts lists for mixed-standard errors and helps identify unknown flanges.
Frequently asked questions about EN (DIN) and ASME flanges
Is Class 150 the same as PN 16?
No. The two are functionally comparable and are matched to each other in purchasing, but mechanically they are incompatible – bolt circle, number of holes and bolt sizes differ. Class 150 also does not mean 150 psi; the permissible pressure depends on material and temperature.
Does an ASME flange fit an EN (DIN) flange?
No, bolt-hole pattern and dimensions differ. For the transition you need a matching counterflange to the other standard or an adapter solution.
What is the difference between DN and NPS?
DN is the dimensionless metric nominal-size designator of the European standards, NPS the inch-based designator of the American ones. DN 50 and NPS 2 belong to the same pipe – the pipe outside diameters of the two worlds are largely identical.
What does raised face (RF) mean?
A raised sealing face – the standard facing to ASME B16.5. The closest EN counterpart is form B1 to EN 1092-1; the two are not identical, so surface roughness has to be checked.
Why does the permissible pressure drop with temperature?
Because material strength decreases with rising temperature. The pressure-temperature tables of the respective standard govern; interpolation is permitted for intermediate temperatures.
What is the difference between old DIN flanges and DIN EN 1092-1?
Many former DIN series were transferred into the European system or replaced by EN types; designations and individual dimensions may have changed. Never substitute an old DIN number with an EN designation without checking.
What does it mean when a flange is “drilled to DIN EN 1092-1”?
Often this only describes the bolt-hole pattern – not the complete standard flange. Material, flange thickness, facing, hub, tolerances, marking and pressure-temperature suitability may deviate; state this clearly in the quotation.
When is the pressure rating alone not enough as a selection criterion?
As soon as relevant external forces and moments, temperature cycling, vacuum, high tightness requirements, special gaskets or non-standard bolting come into play – PN or Class does not automatically cover all piping and installation loads.
When is ASME B16.47 used?
For large steel flanges from NPS 26 to NPS 60 – above the B16.5 range. Series A and Series B are geometrically different and must not be confused.
What information belongs in an unambiguous flange order?
At least standard, flange type, nominal size, PN or Class, facing form, material, pipe connection dimension or wall thickness, weld-end preparation where applicable, and whether an inspection certificate is required. In practice we often receive inquiries stating only DN and pressure rating – for a quotation without queries we additionally need the details listed above.
Find the right flange
You know which standards world your plant needs? Zickwolff supplies flanges in carbon and stainless steel in all common types and pressure ratings – from Germany, across Europe.
Send us your inquiryTechnical basis: DIN EN 1092-1, ASME B16.5, ASME B16.47, ASME B31.3. All information without guarantee – the current standard texts and the manufacturers’ technical data sheets always prevail. Editorially reviewed: August 2026. Standards and manufacturer status considered: July 2026.