Flanges and Bolt Dimensions - Class 150 to 2500 - ASME/ANSI B16.5
Flange dimensions are determined by pipe size and pressure class required for the application. Most of these dimensions have been standardized and published as ASME, MSS, API or other standardization organization specifications.
ASME/ANSI B16.5 provides dimensions and tolerances for flanges in pipe sizes from 1/2" through 24" and in classes ranging 150 through 2500.
| Nominal Pipe Size NPS (inches) | Class 150 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/4 | 3-3/8 | 4 | 1/2 | 2-1/4 |
| 1/2 | 3-1/2 | 4 | 1/2 | 2-3/8 |
| 3/4 | 3-7/8 | 4 | 1/2 | 2-3/4 |
| 1 | 4-1/4 | 4 | 1/2 | 3-1/8 |
| 1-1/4 | 4-5/8 | 4 | 1/2 | 3-1/2 |
| 1-1/2 | 5 | 4 | 1/2 | 3-7/8 |
| 2 | 6 | 4 | 5/8 | 4-3/4 |
| 2-1/2 | 7 | 4 | 5/8 | 5-1/2 |
| 3 | 7-1/2 | 4 | 5/8 | 6 |
| 3-1/2 | 8-1/2 | 8 | 5/8 | 7 |
| 4 | 9 | 8 | 5/8 | 7-1/2 |
| 5 | 10 | 8 | 3/4 | 8-1/2 |
| 6 | 11 | 8 | 3/4 | 9-1/2 |
| 8 | 13-1/2 | 8 | 3/4 | 11-3/4 |
| 10 | 16 | 12 | 7/8 | 14-1/4 |
| 12 | 19 | 12 | 7/8 | 17 |
| 14 | 21 | 12 | 1 | 18-3/4 |
| 16 | 23-1/2 | 16 | 1 | 21-1/4 |
| 18 | 25 | 16 | 1-1/8 | 22-3/4 |
| 20 | 27-1/2 | 20 | 1-1/8 | 25 |
| 24 | 32 | 20 | 1-1/4 | 29-1/2 |
| Nominal Pipe Size NPS (inches) | Class 300 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/4 | 3-3/8 | 4 | 1/2 | 2-1/4 |
| 1/2 | 3-3/4 | 4 | 1/2 | 2-5/8 |
| 3/4 | 4-5/8 | 4 | 5/8 | 3-1/4 |
| 1 | 4-7/8 | 4 | 5/8 | 3-1/2 |
| 1-1/4 | 5-1/4 | 4 | 5/8 | 3-7/8 |
| 1-1/2 | 6-1/8 | 4 | 3/4 | 4-1/2 |
| 2 | 6-1/2 | 8 | 5/8 | 5 |
| 2-1/2 | 7-1/2 | 8 | 3/4 | 5-7/8 |
| 3 | 8-1/4 | 8 | 3/4 | 6-5/8 |
| 3-1/2 | 9 | 8 | 3/4 | 7-1/4 |
| 4 | 10 | 8 | 3/4 | 7-7/8 |
| 5 | 11 | 8 | 3/4 | 9-1/4 |
| 6 | 12-1/2 | 12 | 3/4 | 10-5/8 |
| 8 | 15 | 12 | 7/8 | 13 |
| 10 | 17-1/2 | 16 | 1 | 15-1/4 |
| 12 | 20-1/2 | 16 | 1-1/8 | 17-3/4 |
| 14 | 23 | 20 | 1-1/8 | 20-1/4 |
| 16 | 25-1/2 | 20 | 1-1/4 | 22-1/2 |
| 18 | 28 | 24 | 1-1/4 | 24-3/4 |
| 20 | 30-1/2 | 24 | 1-1/4 | 27 |
| 24 | 36 | 24 | 1-1/2 | 32 |
| Nominal Pipe Size NPS (inches) | Class 400 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/4 | 3-3/8 | 4 | 1/2 | 2-1/4 |
| 1/2 | 3-3/4 | 4 | 1/2 | 2-5/8 |
| 3/4 | 4-5/8 | 4 | 5/8 | 3-1/4 |
| 1 | 4-7/8 | 4 | 5/8 | 3-1/2 |
| 1-1/4 | 5-1/4 | 4 | 5/8 | 3-7/8 |
| 1-1/2 | 6-1/8 | 4 | 3/4 | 4-1/2 |
| 2 | 6-1/2 | 8 | 5/8 | 5 |
| 2-1/2 | 7-1/2 | 8 | 3/4 | 5-7/8 |
| 3 | 8-1/4 | 8 | 3/4 | 6-5/8 |
| 3-1/2 | 9 | 8 | 7/8 | 7-1/4 |
| 4 | 10 | 8 | 7/8 | 7-7/8 |
| 5 | 11 | 8 | 7/8 | 9-1/4 |
| 6 | 12-1/2 | 12 | 7/8 | 10-5/8 |
| 8 | 15 | 12 | 1 | 13 |
| 10 | 17-1/2 | 16 | 1-1/8 | 15-1/4 |
| 12 | 20-1/2 | 16 | 1-1/4 | 17-3/4 |
| 14 | 23 | 20 | 1-1/4 | 20-1/4 |
| 16 | 25-1/2 | 20 | 1-3/8 | 22-1/2 |
| 18 | 28 | 24 | 1-3/8 | 24-3/4 |
| 20 | 30-1/2 | 24 | 1-1/2 | 27 |
| 24 | 36 | 24 | 1-3/4 | 32 |
| Nominal Pipe Size NPS (inches) | Class 600 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/4 | 3-3/8 | 4 | 1/2 | 2-1/4 |
| 1/2 | 3-3/4 | 4 | 1/2 | 2-5/8 |
| 3/4 | 4-5/8 | 4 | 5/8 | 3-1/4 |
| 1 | 4-7/8 | 4 | 5/8 | 3-1/2 |
| 1-1/4 | 5-1/4 | 4 | 5/8 | 3-7/8 |
| 1-1/2 | 6-1/8 | 4 | 3/4 | 4-1/2 |
| 2 | 6-1/2 | 8 | 5/8 | 5 |
| 2-1/2 | 7-1/2 | 8 | 3/4 | 5-7/8 |
| 3 | 8-1/4 | 8 | 3/4 | 6-5/8 |
| 3-1/2 | 9 | 8 | 7/8 | 7-1/4 |
| 4 | 10-3/4 | 8 | 7/8 | 8-1/2 |
| 5 | 13 | 8 | 1 | 10-1/2 |
| 6 | 14 | 12 | 1 | 11-1/2 |
| 8 | 16-1/2 | 12 | 1-1/8 | 13-3/4 |
| 10 | 20 | 16 | 1-1/4 | 17 |
| 12 | 22 | 20 | 1-1/4 | 19-1/4 |
| 14 | 23-3/4 | 20 | 1-3/8 | 20-3/4 |
| 16 | 27 | 20 | 1-1/2 | 23-3/4 |
| 18 | 29-1/4 | 20 | 1-5/8 | 25-3/4 |
| 20 | 32 | 24 | 1-5/8 | 28-1/2 |
| 24 | 37 | 24 | 1-7/8 | 33 |
| Nominal Pipe Size NPS (inches) | Class 900 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/2 | 4-3/4 | 4 | 3/4 | 3-1/4 |
| 3/4 | 5-1/8 | 4 | 3/4 | 3-1/2 |
| 1 | 5-7/8 | 4 | 7/8 | 4 |
| 1-1/4 | 6-1/4 | 4 | 7/8 | 4-3/8 |
| 1-1/2 | 7 | 4 | 1 | 4-7/8 |
| 2 | 8-1/2 | 8 | 7/8 | 6-1/2 |
| 2-1/2 | 9-5/8 | 8 | 1 | 7-1/2 |
| 3 | 9-1/2 | 8 | 7/8 | 7-1/2 |
| 4 | 11-1/2 | 8 | 1-1/8 | 9-1/4 |
| 5 | 13-3/4 | 8 | 1-1/4 | 11 |
| 6 | 15 | 12 | 1-1/8 | 12-1/2 |
| 8 | 18-1/2 | 12 | 1-3/8 | 15-1/2 |
| 10 | 21-1/2 | 16 | 1-3/8 | 18-1/2 |
| 12 | 24 | 20 | 1-3/8 | 21 |
| 14 | 25-1/4 | 20 | 1-1/2 | 22 |
| 16 | 27-3/4 | 20 | 1-5/8 | 24-1/2 |
| 18 | 31 | 20 | 1-7/8 | 27 |
| 20 | 33-3/4 | 20 | 2 | 29-1/2 |
| 24 | 41 | 20 | 2-1/2 | 35-1/2 |
| Nominal Pipe Size NPS (inches) | Class 1500 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/2 | 4-3/4 | 4 | 3/4 | 3-1/4 |
| 3/4 | 5-1/8 | 4 | 3/4 | 3-1/2 |
| 1 | 5-7/8 | 4 | 7/8 | 4 |
| 1-1/4 | 6-1/4 | 4 | 7/8 | 4-3/8 |
| 1-1/2 | 7 | 4 | 1 | 4-7/8 |
| 2 | 8-1/2 | 8 | 7/8 | 6-1/2 |
| 2-1/2 | 9-5/8 | 8 | 1 | 7-1/2 |
| 3 | 10-1/2 | 8 | 1-1/8 | 8 |
| 4 | 12-1/4 | 8 | 1-1/4 | 9-1/2 |
| 5 | 14-3/4 | 8 | 1-1/2 | 11-1/2 |
| 6 | 15-1/2 | 12 | 1-3/8 | 12-1/2 |
| 8 | 19 | 12 | 1-5/8 | 15-1/2 |
| 10 | 23 | 12 | 1-7/8 | 19 |
| 12 | 26-1/2 | 16 | 2 | 22-1/2 |
| 14 | 29-1/2 | 16 | 2-1/4 | 25 |
| 16 | 32-1/2 | 16 | 2-1/2 | 27-3/4 |
| 18 | 36 | 16 | 2-3/4 | 30-1/2 |
| 20 | 38-3/4 | 16 | 3 | 32-3/4 |
| 24 | 46 | 16 | 3-1/2 | 39 |
| Nominal Pipe Size NPS (inches) | Class 2500 | |||
| Diameter of Flange (inches) | No. of Bolts | Diameter of Bolts (inches) | Bolt Circle (inches) | |
| 1/2 | 5-1/4 | 4 | 3/4 | 3-1/2 |
| 3/4 | 5-1/2 | 4 | 3/4 | 3-3/4 |
| 1 | 6-1/4 | 4 | 7/8 | 4-1/4 |
| 1-1/4 | 7-1/4 | 4 | 1 | 5-1/8 |
| 1-1/2 | 8 | 4 | 1-1/8 | 5-3/4 |
| 2 | 9-1/4 | 8 | 1 | 6-3/4 |
| 2-1/2 | 10-1/2 | 8 | 1-1/8 | 7-3/4 |
| 3 | 12 | 8 | 1-1/4 | 9 |
| 4 | 14 | 8 | 1-1/2 | 10-3/4 |
| 5 | 16-1/2 | 8 | 1-3/4 | 12-3/4 |
| 6 | 19 | 8 | 2 | 14-1/2 |
| 8 | 21-3/4 | 12 | 2 | 17-1/4 |
| 10 | 26-1/2 | 12 | 2-1/2 | 21-1/4 |
| 12 | 30 | 12 | 2-3/4 | 24-3/8 |
