ASME B16.5 Flange Dimensions — All Classes
ASME B16.5 covers pipe flanges and flanged fittings in NPS 1/2" through NPS 24" across six pressure classes. Select a class below to view full dimension tables, or use the comparison table to see how NPS 4" flanges scale across classes.
Rated to 19.6 bar (285 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
13 NPS sizes: 1/2" – 12"
View dimensions →Rated to 51.1 bar (740 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
13 NPS sizes: 1/2" – 12"
View dimensions →Rated to 102.1 bar (1480 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
13 NPS sizes: 1/2" – 12"
View dimensions →Rated to 153.2 bar (2220 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
12 NPS sizes: 1/2" – 12"
View dimensions →Rated to 255.3 bar (3705 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
8 NPS sizes: 1/2" – 6"
View dimensions →Rated to 425.5 bar (6170 psi) at ambient temperature — Group 1.1 carbon steel per ASME B16.5.
7 NPS sizes: 1/2" – 4"
View dimensions →NPS 4" Flange: Dimensions by Class
The table below shows how a 4-inch flange grows heavier and larger as the pressure class increases. All dimensions in inches per ASME B16.5.
| Class | OD (in) | Bolts | Bolt Size | Min Thk (in) | |
|---|---|---|---|---|---|
| Class 150 | 9.00" | 8 | 5/8" | 1.06" | Details → |
| Class 300 | 10.75" | 8 | 3/4" | 1.50" | Details → |
| Class 600 | 11.50" | 8 | 1" | 1.88" | Details → |
| Class 900* | 13.38" | 8 | 1-1/4" | 2.44" | Details → |
| Class 1500* | 14.50" | 8 | 1-3/8" | 3.00" | Details → |
| Class 2500* | 15.50" | 8 | 1-1/2" | 3.75" | Details → |
* Class 900, 1500, and 2500 dimensions are reference values. Always verify against the current edition of ASME B16.5.
About ASME B16.5
ASME B16.5 is the American National Standard for pipe flanges and flanged fittings in NPS 1/2 through NPS 24. It defines six pressure classes — 150, 300, 600, 900, 1500, and 2500 — each corresponding to a maximum allowable pressure at a reference temperature for a given material group. Class 150 flanges rated to 285 psi (19.6 bar) at ambient are the most common in process piping; Class 2500 flanges rated to 6170 psi (425 bar) are used in high-pressure service such as wellhead and hydraulic systems.
Dimensions given on this site cover raised face (RF) weld neck flanges as the reference type. Actual dimensions for slip-on, socket weld, blind, and threaded flanges differ; use the Flange Weight Calculator for a full breakdown by type.