ASME B16.21 Non-Metallic Flat Gasket Dimensions
Flat Ring & Full Face Gaskets for ASME B16.5 Flanges
About
ASME B16.21 covers the dimensions for non-metallic flat gaskets used with ASME flanges. The table below combines data from Tables 4.1-4 and 4.1-5 of ASME B16.21-2021, covering gasket dimensions for ASME B16.5 flanges in Class 150 (flat ring and full face) and Classes 300, 600, and 900 (flat ring only).
Access gasket data offline in the field.
Download the Flange Bolt Chart app for instant access to gasket dimensions, flange bolt sizes, and torque values — no internet required.
Non-Metallic Gasket Table
Use the filters below to look up gasket dimensions by NPS. Toggle between imperial and metric units.
21 rows
| NPS | Gasket ID (in) | OD Cl.150 Flat (in) | OD Cl.150 Full (in) | OD Cl.300 Flat (in) | OD Cl.600 Flat (in) | OD Cl.900 Flat (in) |
|---|---|---|---|---|---|---|
| 1/2 | 0.84 | 1.88 | 3.5 | 2.12 | 2.12 | 2.5 |
| 3/4 | 1.06 | 2.25 | 3.88 | 2.62 | 2.62 | 2.75 |
| 1 | 1.31 | 2.62 | 4.25 | 2.88 | 2.88 | 3.12 |
| 1-1/4 | 1.66 | 3 | 4.63 | 3.25 | 3.25 | 3.5 |
| 1-1/2 | 1.91 | 3.38 | 5 | 3.75 | 3.75 | 3.88 |
| 2 | 2.38 | 4.12 | 6 | 4.38 | 4.38 | 5.62 |
| 2-1/2 | 2.88 | 4.88 | 7 | 5.12 | 5.12 | 6.5 |
| 3 | 3.5 | 5.38 | 7.5 | 5.88 | 5.88 | 6.62 |
| 3-1/2 | 4 | 6.38 | 8.5 | 6.5 | 6.38 | — |
| 4 | 4.5 | 6.88 | 9 | 7.12 | 7.62 | 8.12 |
| 5 | 5.56 | 7.75 | 10 | 8.5 | 9.5 | 9.75 |
| 6 | 6.62 | 8.75 | 11 | 9.88 | 10.5 | 11.38 |
| 8 | 8.62 | 11 | 13.5 | 12.12 | 12.62 | 14.12 |
| 10 | 10.75 | 13.38 | 16 | 14.25 | 15.75 | 17.12 |
| 12 | 12.75 | 16.13 | 19 | 16.62 | 18 | 19.62 |
| 14 | 14 | 17.75 | 21 | 19.12 | 19.38 | 20.5 |
| 16 | 16 | 20.25 | 23.5 | 21.25 | 22.25 | 22.62 |
| 18 | 18 | 21.62 | 25 | 23.5 | 24.12 | 25.12 |
| 20 | 20 | 23.88 | 27.5 | 25.75 | 26.88 | 27.5 |
| 22 | 22 | 26 | 29.5 | 27.75 | 28.88 | — |
| 24 | 24 | 28.25 | 32 | 30.5 | 31.12 | 33 |
Data sourced from ASME B16.21-2021, Tables 4.1-4 and 4.1-5.
How to Use This Chart
The table shows gasket inside diameter and outside diameter by pressure class:
- Gasket ID — inside diameter (same across all classes for a given NPS)
- OD Cl.150 Flat — outside diameter for Class 150 flat ring gasket
- OD Cl.150 Full — outside diameter for Class 150 full face gasket (extends to bolt circle)
- OD Cl.300/600/900 Flat — outside diameter for higher-class flat ring gaskets