Flange Dimensions Class 150

Class 150 is the most widely used flange pressure class in the oil and gas industry, covering low-to-moderate pressure services such as utility piping, cooling water, and process lines. The dimensions listed below are per ASME B16.5 and apply to all flange types (weld neck, slip-on, blind, and socket weld) since they share the same outer envelope dimensions, bolt circle, and bolting requirements for a given NPS and class.

Class 150 Flange Dimensions (ASME B16.5)

NPS	Flange OD (inch)	Flange OD (mm)	Thickness (inch)	Thickness (mm)	Bolt Circle Dia (inch)	Bolt Circle Dia (mm)	Bolt Hole Dia (inch)	No. of Bolts	Bolt Dia (inch)	Raised Face Dia (inch)	Raised Face Dia (mm)
1/2	3.50	88.9	0.44	11.2	2.38	60.5	0.62	4	1/2	1.19	30.2
3/4	3.88	98.5	0.50	12.7	2.75	69.9	0.62	4	1/2	1.50	38.1
1	4.25	108.0	0.56	14.2	3.12	79.2	0.62	4	1/2	1.94	49.3
1-1/4	4.62	117.5	0.62	15.7	3.50	88.9	0.62	4	1/2	2.31	58.7
1-1/2	5.00	127.0	0.69	17.5	3.88	98.6	0.62	4	1/2	2.56	65.0
2	6.00	152.4	0.62	15.7	4.75	120.7	0.75	4	5/8	3.31	84.1
2-1/2	7.00	177.8	0.75	19.1	5.50	139.7	0.75	4	5/8	3.94	100.1
3	7.50	190.5	0.75	19.1	6.00	152.4	0.75	4	5/8	4.62	117.3
3-1/2	8.50	215.9	0.75	19.1	7.00	177.8	0.75	8	5/8	5.25	133.4
4	9.00	228.6	0.94	23.8	7.50	190.5	0.75	8	5/8	5.31	134.9
5	10.00	254.0	0.94	23.8	8.50	215.9	0.88	8	3/4	6.44	163.6
6	11.00	279.4	1.00	25.4	9.50	241.3	0.88	8	3/4	7.56	192.0
8	13.50	342.9	1.12	28.4	11.75	298.5	0.88	8	3/4	9.19	233.4
10	16.00	406.4	1.19	30.2	14.25	362.0	1.00	12	7/8	11.31	287.3
12	19.00	482.6	1.25	31.8	17.00	431.8	1.00	12	7/8	13.00	330.2
14	21.00	533.4	1.38	35.1	18.75	476.3	1.12	12	1	14.00	355.6
16	23.50	596.9	1.44	36.6	21.25	539.8	1.12	16	1	16.00	406.4
18	25.00	635.0	1.56	39.6	22.75	577.9	1.25	16	1-1/8	18.00	457.2
20	27.50	698.5	1.69	42.9	25.00	635.0	1.25	20	1-1/8	20.00	508.0
24	32.00	812.8	1.62	41.1	29.50	749.3	1.38	20	1-1/4	23.75	603.2

All dimensions per ASME B16.5-2020. Thickness values are minimum for raised face (RF) flanges; the raised face height of 1.6 mm (1/16 in) is included in the thickness. Bolt hole diameter is 1/8 inch (3.2 mm) larger than the nominal bolt diameter.

Notes

• Applicable flange types: The OD, bolt circle, bolt holes, number of bolts, and bolt diameter values apply to all ASME B16.5 Class 150 flange types, including weld neck (WN), slip-on (SO), blind (BL), socket weld (SW), lap joint (LJ), and threaded (THD) flanges.
• Thickness variations: While the outer envelope dimensions are the same, the minimum flange thickness may vary slightly between flange types. The values in the table above represent the standard thickness for weld neck flanges; slip-on and socket weld flanges have slightly different thicknesses per ASME B16.5 Table 18.
• Raised face dimensions: The raised face (RF) is standard for Class 150 flanges and has a height of 1.6 mm (1/16 inch). The raised face diameter shown is the contact area for the gasket.
• Bolt specifications: Bolts are stud bolts per ASME B16.5. Bolt holes straddle the natural centerlines of the flange (they are not placed directly on the centerlines).
• Pressure rating: Class 150 carbon steel (ASTM A105) flanges are rated for approximately 19.6 bar (285 psi) at ambient temperature. The rating decreases at elevated temperatures per the ASME B16.5 pressure-temperature tables.
• Reference standard: ASME B16.5-2020, Pipe Flanges and Flanged Fittings, NPS 1/2 Through NPS 24 Metric/Inch Standard.