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Flange Dimensions Reference

Raised-face flange dimensions for ASME B16.5 (NPS 1/2" - 24"), ASME B16.47 Series A (NPS 26" - 60"), and EN 1092-1 Type 11 welding-neck (DN 10 - DN 600, PN 6 / 10 / 16 / 25 / 40). The selector below switches between standards and pressure classes; dimensions can be displayed in inches or millimetres.

Flange Dimension Table
NPSPipe OD (in)Flange OD (in)Thickness (in)RF OD (in)Bolt Circle (in)BoltsBoltHole (in)
1/2"0.843.50.441.382.3840.5"0.625
3/4"1.053.880.51.692.7540.5"0.625
1"1.3154.250.5623.1240.5"0.625
1-1/4"1.664.620.622.53.540.5"0.625
1-1/2"1.950.692.883.8840.5"0.625
2"2.37560.753.624.7540.625"0.75
2-1/2"2.87570.884.125.540.625"0.75
3"3.57.50.945640.625"0.75
3-1/2"48.50.945.5780.625"0.75
4"4.590.946.197.580.625"0.75
5"5.563100.947.318.580.75"0.875
6"6.6251118.59.580.75"0.875
8"8.62513.51.1210.6211.7580.75"0.875
10"10.75161.1912.7514.25120.875"1
12"12.75191.251517120.875"1
14"14211.3816.2518.75121"1.125
16"1623.51.4418.521.25161"1.125
18"18251.562122.75161.125"1.25
20"2027.51.692325201.125"1.25
24"24321.8827.2529.5201.25"1.375

Thickness includes the 1/16" raised face for Class 150/300 and excludes the 1/4" raised face for Class 600 and higher (ASME convention). Bolt hole = bolt diameter + 1/8". The Bolt column always shows the nominal bolt designation in inches.

For design and procurement, always verify against the current edition of the standard (ASME B16.5).

About These Standards

ASME B16.5 covers pipe flanges and flanged fittings for NPS 1/2 through NPS 24 in pressure classes 150, 300, 600, 900, 1500, and 2500. These are the most widely used flanges in process piping, refineries, and power plants.

ASME B16.47 Series A (formerly MSS SP-44) covers large-diameter steel flanges from NPS 26 through NPS 60. Series A flanges are commonly used in petroleum, chemical, and water industries for large-bore piping systems.

EN 1092-1 is the European/metric standard for circular flanges for pipes, valves, fittings and accessories. It defines flanges by PN designation (nominal pressure in bar at 20 °C) rather than ASME's pressure class. The EN tables here are Type 11 welding-neck flanges — the dominant industrial type. Bolts are sized by metric thread (M10 through M36); the bolt hole diameter is the actual through-hole, not the bolt diameter.

All dimensions shown are for raised-face (RF) flanges. Actual bore dimensions depend on pipe schedule (see our pipe schedules reference) and are not included in these tables. For choosing the gasket that sits between these flanges, see our flange gasket selection guide.

Column Definitions
NPS / DN
Nominal Pipe Size (ASME) or Diamètre Nominal (EN)
Pipe OD
Pipe outside diameter
Flange OD
Flange outside diameter
Thickness
Minimum flange thickness
RF OD
Raised face outside diameter
Bolt Circle
Bolt circle diameter
Bolts
Number of bolt holes
Bolt
Bolt designation (fractional inches for ASME, metric thread for EN)
Hole
Bolt hole diameter (through-hole)

Frequently Asked Questions

What is the difference between ASME B16.5 and B16.47?
ASME B16.5 covers pipe flanges from NPS 1/2 to NPS 24 in pressure classes 150 through 2500. ASME B16.47 covers large diameter flanges from NPS 26 to NPS 60 in two series: Series A (based on MSS SP-44) and Series B (based on API 605). Series A flanges are generally heavier and more common in high-integrity applications, but note that for Class 300 from NPS 38 to 60 the two series are identical in the current edition of the standard.
What do the pressure classes (150, 300, 600, etc.) mean?
Pressure classes define the pressure-temperature rating of a flange. Class 150 does not mean 150 psi — the actual rating depends on the flange material and operating temperature. For example, an A105 carbon steel Class 150 flange is rated to 285 psi at ambient temperature but only 170 psi at 500 degrees F. The ASME B16.5 tables provide exact ratings per material group.
What is a raised face (RF) flange?
A raised face flange has a small raised area around the bore where the gasket seats. The raised face height is 1/16 inch (1.6 mm) for Class 150 and 300, and 1/4 inch (6.4 mm) for Class 600 and above. Per ASME B16.5 convention, the thickness values in this table include the 1/16 inch raised face for Class 150 and 300, and exclude the 1/4 inch raised face for Class 600 and higher. Other face types include flat face (FF), ring-type joint (RTJ), and tongue-and-groove.
How do I select the right flange class for my application?
Start with your maximum operating pressure and temperature. Look up the pressure-temperature rating table in ASME B16.5 for your flange material group to find the minimum class that covers your conditions. Also consider upset conditions, hydrostatic test pressure, and whether the piping specification requires a higher class. Most process plant piping uses Class 150 or 300.
What is the bolt circle diameter?
The bolt circle diameter is the diameter of the imaginary circle that passes through the centre of all bolt holes. It is one of the critical dimensions for flange alignment. When two flanges are bolted together, their bolt circle diameters must match. This dimension, along with the number and size of bolt holes, is standardised by ASME B16.5 (and EN 1092-1) for each NPS/DN and pressure class.
What is the difference between ASME B16.5 and EN 1092-1?
ASME B16.5 (North American) and EN 1092-1 (European/metric) are not interchangeable. They use different size systems (NPS vs DN), different pressure-class designations (Class 150/300/600… vs PN 6/10/16/25/40…), different bolt patterns, and different dimensions in inches vs millimetres. A Class 150 flange and a PN 16 flange may both rate to similar pressure but have different OD, bolt circle, and bolt count — so they cannot be bolted directly to each other without an adapter. EN 1092-1 also defines multiple flange types (Type 01 slip-on, Type 11 welding-neck, Type 32/33 lap joint, etc.); the dimensions on this page are for Type 11 welding-neck, the dominant industrial type.
How do PN ratings compare to ASME pressure classes?
PN (Pression Nominale) is the nominal pressure in bar at 20 °C; ASME pressure class is a dimensionless number related to allowable working pressure at temperature. There's no exact equivalence — PN 16 is roughly comparable to Class 150 for low-temperature service, PN 25 to Class 300, and PN 40 to Class 300 / 400. The actual pressure-temperature rating depends on flange material; consult ASME B16.5 Table 2 or EN 1092-1 Annex G for exact ratings at your operating temperature. Don't size by class number alone.

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