Standard reference · interchangeability
ASME, EN and JIS flanges: same nominal size is not the same flange
A DN 100 flange exists in all three systems, but its outside diameter, bolt circle and bolt size are different. This page puts the three dimension sets side by side using our transcribed tables, so you can see exactly where a swap fails before you order.
All dimensions are millimetres, weld-neck flanges, ASME B16.5 Class 150 against EN 1092-1 PN16 and JIS B2220 10K — the three ratings buyers most often treat as “equivalent”.
Weld-neck flanges · class 150 / PN16 / 10K
| Size | ASME OD mm | EN OD mm | JIS OD mm | OD difference mm |
|---|---|---|---|---|
| 1″ | 108 | 115 | 125 | 17 |
| 1½″ | 127 | 150 | 140 | 23 |
| 2″ | 152.4 | 165 | 155 | 12.6 |
| 2½″ | 177.8 | 185 | 175 | 10 |
| 3″ | 190.5 | 200 | 185 | 15 |
| 4″ | 228.6 | 220 | 210 | 18.6 |
| 6″ | 279.4 | 285 | 280 | 5.6 |
| 8″ | 342.9 | 340 | 330 | 12.9 |
| 12″ | 482.6 | 460 | 445 | 37.6 |
| 16″ | 596.9 | 580 | 560 | 36.9 |
| 20″ | 698.5 | 715 | 675 | 40 |
| 24″ | 812.8 | 840 | 795 | 45 |
OD difference is the spread between the largest and smallest outside diameter at that nominal size. ASME dimensions are converted from inches; EN and JIS are metric. “—” means the size is not published in that standard/rating combination.
Weld-neck flanges · class 150 / PN16 / 10K
| Size | ASME bolt circle mm | EN bolt circle mm | JIS bolt circle mm | Bolt circle spread mm | ASME bolts | EN bolts | JIS bolts |
|---|---|---|---|---|---|---|---|
| 1″ | 79.2 | 85 | 90 | 10.8 | 4 × Ø15.9 | 4 × Ø14 | 4 × Ø19 |
| 1½″ | 98.6 | 110 | 105 | 11.4 | 4 × Ø15.9 | 4 × Ø18 | 4 × Ø19 |
| 2″ | 120.7 | 125 | 120 | 5 | 4 × Ø19.1 | 4 × Ø18 | 4 × Ø19 |
| 2½″ | 139.7 | 145 | 140 | 5.3 | 4 × Ø19.1 | 8 × Ø18 | 4 × Ø19 |
| 3″ | 152.4 | 160 | 150 | 10 | 4 × Ø19.1 | 8 × Ø18 | 8 × Ø19 |
| 4″ | 190.5 | 180 | 175 | 15.5 | 8 × Ø19.1 | 8 × Ø18 | 8 × Ø19 |
| 6″ | 241.3 | 240 | 240 | 1.3 | 8 × Ø22.2 | 8 × Ø22 | 8 × Ø23 |
| 8″ | 298.5 | 295 | 290 | 8.5 | 8 × Ø22.2 | 12 × Ø22 | 12 × Ø23 |
| 12″ | 431.8 | 410 | 400 | 31.8 | 12 × Ø25.4 | 12 × Ø26 | 16 × Ø25 |
| 16″ | 539.8 | 525 | 510 | 29.8 | 16 × Ø28.6 | 16 × Ø30 | 16 × Ø27 |
| 20″ | 635 | 650 | 620 | 30 | 20 × Ø31.8 | 20 × Ø33 | 20 × Ø27 |
| 24″ | 749.3 | 770 | 730 | 40 | 20 × Ø34.9 | 20 × Ø36 | 24 × Ø33 |
Bolt circle spread is the difference between the largest and smallest bolt circle at that nominal size — far larger than the bolt-hole clearance, which is why the flanges do not interchange. Bolt strings are bolt count × hole diameter.
What the table means in practice
At small sizes the three systems can be within a few millimetres of each other, which is why a flange is sometimes forced onto the wrong bolts on site. At DN 100 the bolt circles are 190.5 mm, 180 mm and 175 mm — a 15.5 mm spread, far more than any hole clearance. At DN 300 the spread grows past 20 mm. No amount of bolt hole clearance closes that gap: the joint either does not assemble or is loaded by the bolts instead of the gasket.
The bolt count is not a reliable identifier either. Many sizes share the same number of bolts across all three standards, while the circle and hole diameter differ. Identify a flange by its standard family and measure the bolt circle, not by counting bolts.
Class, PN and K are ratings, not dimensions
The table below is a budgetary comparison of ambient pressure duty only. It is useful for shortlisting a standard family; it is not a conversion table.
Pressure duty only
| ASME class | Ambient rating, A105 / group 1.1 | Nearest EN PN | Nearest JIS K | Typical service |
|---|---|---|---|---|
| 150 | 19.6 bar (285 psi) | PN20 | 5K / 10K | Low-pressure water, utility, HVAC |
| 300 | 51.0 bar (740 psi) | PN50 | 10K / 16K | Medium-pressure process, steam |
| 400 | 68.2 bar (990 psi) | PN64 | 16K | Between Class 300 and 600 |
| 600 | 102.1 bar (1,480 psi) | PN100 | 16K / 20K | High-pressure process, hydrocarbons |
| 900 | 153.1 bar (2,220 psi) | PN150 | 20K / 30K | High-pressure and severe service |
| 1500 | 255.5 bar (3,705 psi) | PN250 | 30K | Very high pressure, small bore |
| 2500 | 425.5 bar (6,170 psi) | PN420 | — | Extreme pressure, NPS ≤ 12 |
ASME values are for ASTM A105 (material group 1.1) at 38 °C. EN PN is nominal pressure for material group 1 at 20 °C. JIS K ratings are kgf/cm² nominal. All three derate with temperature; read the actual p/T table for your material and design temperature.
DN, NPS and JIS “A” nominal sizes
The nominal size is the one thing the three systems do share, roughly. Use this to find the equivalent size, then read the dimensions from the standard you are actually buying.
Nominal size reference
| DN | NPS | JIS nominal size |
|---|---|---|
| 15 | 1/2″ | 15A |
| 20 | 3/4″ | 20A |
| 25 | 1″ | 25A |
| 32 | 1-1/4″ | 32A |
| 40 | 1-1/2″ | 40A |
| 50 | 2″ | 50A |
| 65 | 2-1/2″ | 65A |
| 80 | 3″ | 80A |
| 90 | 3-1/2″ | 90A |
| 100 | 4″ | 100A |
| 125 | 5″ | 125A |
| 150 | 6″ | 150A |
| 200 | 8″ | 200A |
| 250 | 10″ | 250A |
| 300 | 12″ | 300A |
| 350 | 14″ | 350A |
| 400 | 16″ | 400A |
| 450 | 18″ | 450A |
| 500 | 20″ | 500A |
| 600 | 24″ | 600A |
| 650 | 26″ | 650A |
| 750 | 30″ | 750A |
| 900 | 36″ | 900A |
| 1,050 | 42″ | 1050A |
| 1,200 | 48″ | 1200A |
Nominal size is a label, not a dimension. Above DN 600, ASME B16.47 (NPS 26–60) takes over from B16.5.
How to order a flange that will actually fit
- Quote the standard and edition, plus the series for ASME B16.47 (Series A or B).
- Give the nominal size in the standard’s own units, e.g. NPS 4, DN 100 or 100A.
- State the class, PN or K rating — never convert it on the purchase order.
- State the facing: RF, FF, RTJ, or tongue and groove, and the surface finish where specified.
- Give the material and any impact-testing or NACE requirement.
- If you are replacing an existing part, measure the bolt circle and bolt hole diameter and include a photo with a tape measure.
Interchangeability questions
Will a PN16 flange bolt to an ASME Class 150 flange?
No. Even where the outside diameters look close, the bolt circle, bolt count and hole diameter are set by each standard family. At DN 100 / 4″, ASME B16.5 Class 150 has a 190.5 mm bolt circle while EN 1092-1 PN16 has 180 mm and JIS B2220 10K has 175 mm, so the holes do not line up. Use a mating flange from the same standard, or an adapter spool.
Is JIS 10K the same as ASME Class 150?
They are close in pressure duty — 10K is nominally 1 MPa and Class 150 is about 1.96 MPa at ambient — but the dimensions differ. JIS uses millimetre outside diameters and its own bolt pattern, and its rating derates differently with temperature. A JIS 10K flange will not bolt to a Class 150 flange of the same nominal size.
Which standard should I specify for a replacement flange?
Specify the standard of the mating flange, not the pressure that looks equivalent. Read the bolt circle and bolt count from the existing part (or the drawing), then quote the standard, series (for B16.47), size, class/PN/K, facing and material. When in doubt, send a photo with a tape measure across the bolt circle.
Do ASME classes and PN ratings mean the same pressure at temperature?
Only approximately at ambient temperature. Both systems derate with temperature, but the curves and material groups differ, and NEITHER can be converted by a fixed factor. Read the allowable pressure for the specific material group and design temperature from the standard you are using.
Where these numbers come from
Dimensions are taken from the site’s transcribed standard tables (ASME B16.5, EN 1092-1, JIS B2220) and cross-checked against the dimensional datasets used for the size pages. Ratings are from the standards’ pressure–temperature tables; see the individual standard pages for material-group detail and edition notes. Verify the edition named in your purchase specification before quoting a critical part.