SDR Explained: Why Wall Thickness Matters in HDPE Pipes
SDR (Standard Dimension Ratio) determines wall thickness and pressure rating. This guide explains what SDR means, the 10 classes in IS 4984:2016, and how to use SDR to select the right pipe.
Two HDPE pipes can look identical — same diameter, same colour — but have completely different wall thicknesses and pressure ratings. The key to understanding this is SDR: Standard Dimension Ratio.
What is SDR?
SDR = Outside Diameter (OD) ÷ Minimum Wall Thickness. For example: A 110mm OD pipe with 10mm wall thickness has SDR = 110 ÷ 10 = 11. This is designated SDR 11.
The Golden Rule: Lower SDR = Thicker Wall = Higher Pressure
- SDR 41 → Very thin wall → Low pressure (PN 2 to PN 2.5)
- SDR 17 → Medium wall → Standard pressure (PN 6)
- SDR 11 → Thick wall → High pressure (PN 10)
- SDR 6 → Thickest wall → Very high pressure (PN 20)
All 10 SDR Classes in IS 4984:2016
| SDR Class | PN (PE 80) | PN (PE 100) | Typical Application |
|---|---|---|---|
| SDR 41 | PN 2.5 | — | Gravity-fed water mains, low head |
| SDR 33 | PN 3.2 | PN 4 | Low pressure distribution |
| SDR 26 | PN 4 | PN 5 | Rural water supply gravity systems |
| SDR 21 | PN 5 | PN 6 | Light pressure irrigation |
| SDR 17 | PN 6 | PN 8 | Agricultural mains, sprinkler systems |
| SDR 13.6 | PN 8 | PN 10 | Town water supply standard |
| SDR 11 | PN 10 | PN 12.5 | High pressure water supply |
| SDR 9 | PN 12.5 | PN 16 | Municipal supply and industrial |
| SDR 7.4 | PN 16 | PN 20 | High pressure industrial |
| SDR 6 | PN 20 | PN 20 | Very high pressure (PE 100 only) |
Important: The PN rating depends on both SDR AND material grade. A PE 100 pipe has a higher pressure rating than a PE 80 pipe of the same SDR and size. Always check both values on the pipe label.
Wall Thickness Example — 110mm OD Pipe
| SDR | OD (mm) | Wall Thickness | PN (PE 80) |
|---|---|---|---|
| SDR 17 | 110 | 6.6 mm | PN 6 |
| SDR 13.6 | 110 | 8.1 mm | PN 8 |
| SDR 11 | 110 | 10.0 mm | PN 10 |
| SDR 9 | 110 | 12.3 mm | PN 12.5 |
| SDR 7.4 | 110 | 14.9 mm | PN 16 |
How to Read an HDPE Pipe Label Correctly
A correctly marked IS 4984 pipe shows all of the following in the print line: Material grade (PE 100) / Pressure rating (PN 10) / Nominal diameter (DN 110) / SDR (SDR 11) / Standard (IS 4984:2016) / Manufacturer name / BIS licence number. If SDR or PN is missing, the pipe may not be genuine ISI-certified material.
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