When sourcing galvanized steel pipes internationally, one of the most common headaches for procurement managers and engineers is translating dimensional standards. A blueprint might specify a "2-inch pipe" (NPS), while a Chinese supplier quotes a "DN50 pipe", leaving you wondering: What is the actual Outer Diameter (OD)? Will it fit my fittings?
Choosing the wrong dimension can lead to costly installation failures and project delays.
As a premier manufacturer of high-quality steel pipes, we have created this definitive sizing and application guide. Below, you will find the exact conversions from DN to actual Outer Diameter (OD), practical applications for each size, and crucial quality metrics you must check before placing your next order.
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The Ultimate Galvanized Pipe Sizing Chart (DN15 to DN100)
Understanding the terms:
- DN (Nominal Diameter): The international metric standard designation for pipe sizes. It is a reference number used for standardization, not the exact measurable physical dimension.
- NPS / Inch: Nominal Pipe Size, the North American standard.
- OD (Outer Diameter): The actual physical outside measurement of the pipe, crucial for threading and grooving.
| Metric Standard (DN) | Imperial Standard (NPS / Inch) | Asian Sourcing Term | Actual Outer Diameter (OD) |
| DN15 | 1/2" | 4分管 | 21.3 mm |
| DN20 | 3/4" | 6分管 | 26.8 mm |
| DN25 | 1" | 1寸管 | 33.5 mm |
| DN32 | 1 1/4" (1.25") | 1寸2管 | 42.25 mm |
| DN40 | 1 1/2" (1.5") | 1寸半管 | 48.0 mm |
| DN50 | 2" | 2寸管 | 60.0 mm |
| DN65 | 2 1/2" (2.5") | 2寸半管 | 75.5 mm |
| DN80 | 3" | 3寸管 | 88.5 mm |
| DN100 | 4" | 4寸管 | 114.0 mm |
Which Pipe Size Do You Need? (Common Engineering Applications)
Knowing the outer diameter is only half the battle. Matching the exact DN size to your specific engineering environment is critical for fluid dynamics and structural integrity.
1. Small Diameter Pipes (DN15 – DN25 / 21.3mm - 33.5mm)
Best For: Indoor potable water supply, light structural frameworks, greenhouse construction, and low-pressure compressed air lines.
Engineering Note: These sizes are highly malleable and frequently threaded for quick residential and commercial plumbing connections.
2. Medium Diameter Pipes (DN32 – DN50 / 42.25mm - 60.0mm)
Best For: Fire sprinkler systems, gas transmission pipelines, and heavy-duty scaffolding tubes.
Engineering Note: DN50 (2-inch) is the undisputed workhorse for fire protection systems. They demand high hydrostatic pressure ratings and thick, uniform zinc coatings to prevent internal scaling.
3. Large Diameter Pipes (DN65 – DN100 / 75.5mm - 114.0mm)
Best For: Industrial fluid transmission, HVAC chilled water lines, municipal water mains, and heavy structural column supports.
Engineering Note: These larger pipes are often grooved (using Victaulic couplings) rather than threaded, ensuring fast and leak-proof installation in mega-infrastructure projects.
Beyond Dimensions: How to Avoid Substandard Galvanized Pipes
Getting the OD (Outer Diameter) right is easy. But dimensions alone do not guarantee a 20-year lifespan. When evaluating quotes from Chinese suppliers, ensure your pipes meet the following strict criteria:
1. Wall Thickness Matters (SCH & BS1387): A DN50 pipe can have an OD of 60mm, but its wall thickness determines its pressure rating. We manufacture strictly to BS1387 (Light/Medium/Heavy), ASTM A53 (SCH40/SCH80), and EN 10255 standards. Never accept "under-thickness" pipes that compromise safety.
2. Hot-Dipped vs. Pre-Galvanized: Do not fall for cheap pre-galvanized tubes if your project is outdoors. We specialize in Hot-Dipped Galvanization (HDG), delivering a thick, metallurgically bonded zinc coating of 220g/m² to 500g/m². This guarantees decades of rust-free service even in highly corrosive environments.
3. Custom End Finishes: We don't just sell plain-end pipes. To save you massive on-site labor costs, we supply pipes ready for assembly: Threaded & Coupled (BSPT/NPT), Grooved (for fire fighting), and Beveled for welding.
Galvanized rigid steel conduit dimensions
Available in sizes 1/2(16) -6 (155)
|
Trade Size |
Metric Designator |
Outside Diameter |
Nominal wall Thickness |
Approximate Weight Per 100 FT. (30.5M) |
Quantity in Master Bundle |
||||
|
in |
mm |
in |
mm |
lb |
kg |
ft |
m |
||
|
1/2 |
16 |
0.840 |
21.34 |
0.104 |
2.64 |
82 |
37.5 |
2500 |
762.5 |
|
3/4 |
21 |
1.050 |
26.67 |
0.107 |
2.72 |
109 |
49.4 |
2000 |
610.0 |
|
1 |
27 |
1.315 |
33.40 |
0.126 |
3.20 |
161 |
73.0 |
1250 |
381.3 |
|
1 1/4 |
35 |
1.660 |
42.16 |
0.133 |
3.38 |
218 |
98.9 |
900 |
274.5 |
|
1 1/2 |
41 |
1.900 |
48.26 |
0.138 |
3.51 |
263 |
119.3 |
800 |
244.0 |
|
2 |
53 |
2.375 |
60.33 |
0.146 |
3.71 |
350 |
158.8 |
600 |
183.0 |
|
2 1/2 |
63 |
2.875 |
73.03 |
0.193 |
4.90 |
559 |
253.6 |
370 |
112.9 |
|
3 |
78 |
3.500 |
88.90 |
0.205 |
5.21 |
727 |
329.8 |
300 |
91.5 |
|
3 1/2 |
91 |
4.000 |
101.60 |
0.215 |
5.46 |
880 |
399.2 |
250 |
76.3 |
|
4 |
103 |
4.500 |
114.30 |
0.225 |
5.72 |
1030 |
467.2 |
200 |
61.0 |
|
5 |
129 |
5.563 |
141.30 |
0.245 |
6.22 |
1520 |
689.5 |
150 |
45.8 |
|
6 |
155 |
6.625 |
168.28 |
0.266 |
6.76 |
1785 |
809.7 |
100 |
30.5 |
Finalizing the BOM (Bill of Materials) for your next pipeline or scaffolding project?
Stop guessing and overpaying. We maintain over 10,000 tons of ready stock for all standard sizes from DN15 to DN100. Tell us your required OD, wall thickness, and end-finish.
[Click Here to Download our 2026 Galvanized Pipe Dimension & Price List PDF]
(Our engineering team will respond with a factory-direct CIF quote within 2 hours!)
