Flange dimensions are standardized, so a Class 300 weld neck flange from any compliant mill bolts up identically. Below are the key dimensions for the most requested ASME B16.5 classes. For full charts including DN sizes, DIN/EN and JIS tables, request our dimension sheet.
How to Read a Flange Size Chart
- NPS / DN – nominal pipe size (inch / mm)
- OD – outside diameter of the flange ring
- Bolt circle – diameter of the bolt-hole pattern centerline
- Bolts – number and diameter of stud bolts
- Thickness – flange ring thickness (min)
- OAL/Hub – overall length (weld neck) incl. hub
ASME B16.5 Class 150 Weld Neck (key dimensions, inch)
| NPS | Flange OD | Bolt Circle | Bolts (No. x dia) | Thickness |
|---|---|---|---|---|
| 1/2 | 3.50 | 2.38 | 4 x 0.50 | 0.44 |
| 1 | 4.25 | 3.12 | 4 x 0.50 | 0.50 |
| 2 | 6.00 | 4.75 | 4 x 0.62 | 0.75 |
| 4 | 9.00 | 7.50 | 8 x 0.75 | 0.88 |
| 6 | 11.00 | 9.50 | 8 x 0.88 | 0.98 |
| 8 | 13.50 | 11.75 | 8 x 0.88 | 1.12 |
| 12 | 19.00 | 17.00 | 12 x 1.00 | 1.25 |
| 24 | 32.00 | 29.50 | 20 x 1.25 | 1.81 |
Class 300 Weld Neck (key dimensions, inch)
| NPS | Flange OD | Bolt Circle | Bolts (No. x dia) | Thickness |
|---|---|---|---|---|
| 1/2 | 3.75 | 2.62 | 4 x 0.50 | 0.56 |
| 2 | 6.50 | 5.00 | 8 x 0.62 | 0.88 |
| 4 | 10.00 | 7.88 | 8 x 0.88 | 1.19 |
| 8 | 15.00 | 13.00 | 12 x 1.00 | 1.50 |
| 12 | 20.50 | 18.25 | 16 x 1.12 | 1.75 |
Common Flange Sizes by Application
- Small bore instrumentation: 1/2″ – 2″ (often socket weld)
- Process piping: 2″ – 12″ (weld neck RF is the workhorse)
- Utility water/air: 2″ – 24″ (slip-on or plate flanges)
- Large diameter transmission: 26″ – 60″ per ASME B16.47
Flange Size FAQs
How do I measure a flange?
Measure flange OD, bolt circle, bolt hole diameter and count, and ring thickness – those four values identify the size and class in the standard tables.
Are DIN and ANSI flanges interchangeable?
No – drilling patterns and pressure ratings differ (PN vs Class). Never mix standards in one joint; adapt with a transition piece if needed.
We manufacture to your specified size and class – send us your dimension list for a fast quote.