Flange Size Charts: How to Read ASME B16.5 Dimension Tables
Flange Size Charts: Complete Guide to ASME B16.5 Dimensions
Published: April 10, 2026 | Category: Technical Guide
Introduction
A flange size chart is your roadmap to selecting the right flange. ASME B16.5 organizes dimensions by Nominal Pipe Size (NPS) and Pressure Class (150-2500).
Key Dimensions
- Outside Diameter (OD) – Overall flange diameter
- Bolt Circle Diameter (BCD) – Circle through bolt hole centers
- Number of Bolt Holes – Increases with pressure class
- Flange Thickness – Increases with pressure
- Raised Face Height – 1/16″ for 150-300#, 1/4″ for 400#+
Sample Table (NPS 4″)
| Class | OD | BCD | Bolts | Thickness |
|---|---|---|---|---|
| 150# | 9.00″ | 7.50″ | 8×5/8″ | 0.88″ |
| 300# | 10.00″ | 8.50″ | 8×3/4″ | 1.12″ |
| 600# | 10.75″ | 9.25″ | 12×3/4″ | 1.38″ |
How to Use a Flange Chart
- Identify pipe size (NPS)
- Determine pressure class
- Look up dimensions
- Cross-check mating components
Common Mistakes
- Confusing NPS with actual dimensions
- Ignoring pressure class differences
- Forgetting raised face height
- Mixing metric and imperial
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