A quick lookup for common Class 150 flange drilling dimensions, sourced from Texas Flange. All dimensions below are inches; NPS is the nominal pipe size, not the flange outside diameter.
Class 150 quick-reference chart
| NPS | Outside diameter | Bolt circle diameter | Hole count | Hole diameter |
|---|---|---|---|---|
| ½ | 3.50 | 2.38 | 4 | 0.62 |
| ¾ | 3.88 | 2.75 | 4 | 0.62 |
| 1 | 4.25 | 3.12 | 4 | 0.62 |
| 1¼ | 4.62 | 3.50 | 4 | 0.62 |
| 1½ | 5.00 | 3.88 | 4 | 0.62 |
| 2 | 6.00 | 4.75 | 4 | 0.75 |
| 2½ | 7.00 | 5.50 | 4 | 0.75 |
| 3 | 7.50 | 6.00 | 4 | 0.75 |
| 3½ | 8.50 | 7.00 | 8 | 0.75 |
| 4 | 9.00 | 7.50 | 8 | 0.75 |
| 5 | 10.00 | 8.50 | 8 | 0.88 |
| 6 | 11.00 | 9.50 | 8 | 0.88 |
| 8 | 13.50 | 11.75 | 8 | 0.88 |
| 10 | 16.00 | 14.25 | 12 | 1.00 |
| 12 | 19.00 | 17.00 | 12 | 1.00 |
Values retain the source’s displayed rounding. Hole diameter is not bolt diameter.
Reading the drilling pattern
The outside diameter describes the flange perimeter. The bolt circle passes through the centers of the bolt holes. Count the holes and measure their diameter separately. The illustration shows an NPS 4 Class 150 drilling pattern; its bore and facing are omitted.
Before specifying a flange
Class 150 is a pressure-class designation, not a fixed 150 psi pressure rating. Pressure capability depends on material and temperature. Confirm the flange type, facing, bore, material, gasket, fasteners, and applicable standard with the equipment supplier. This chart covers drilling dimensions only; it does not establish pressure suitability or interchangeability.
Full charts and engineering documents
- Texas Flange: full Class 150 dimension table
- Texas Flange: one-page Class 150 chart (PDF)
- Texas Flange: other pressure-class charts
- Texas Flange: CAD and 3D flange drawings
- ASME B16.5: standard scope and purchase information
Reference checked October 4, 2026. ANSI is a common search term; the referenced dimensional standard is ASME B16.5. Texas Flange supplies the linked reference charts; this site is not affiliated with Texas Flange.
