{"id":17046,"date":"2026-01-13T06:35:56","date_gmt":"2026-01-13T06:35:56","guid":{"rendered":"https:\/\/pandapipe.com\/?p=17046"},"modified":"2026-09-02T06:47:13","modified_gmt":"2026-09-02T06:47:13","slug":"outer-diameter","status":"publish","type":"post","link":"https:\/\/pandapipe.com\/it\/blog\/outer-diameter\/","title":{"rendered":"Diametro esterno - Un'analisi completa delle dimensioni del diametro esterno dei tubi in acciaio"},"content":{"rendered":"\t\t
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All pipes mentioned in this article are sold by PANDAPIPE.<\/h4>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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You’ve undoubtedly encountered the term \u201csteel pipe outer diameter\u201d on construction sites, in workshops, or within project proposals. Many initially dismiss it as just a \u201cdimensional figure,\u201d but only after hitting snags in actual projects do they realize this number often determines whether a pipeline is functional, installable, or prone to issues. Those working with steel pipes at PANDAPIPE understand that outer diameter isn’t merely a nice-to-have specification in a parameter chart\u2014it’s critical to the project’s successful implementation.<\/div><\/article>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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What is Outer Diameter<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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What is the outside diameter<\/span>? Simply put, outer diameter (OD) (external diameter) <\/strong>is the straight-line distance between the outer walls of a steel pipe. It’s typically measured in millimeters, though inches are also used. Don’t underestimate this number\u2014it’s not just about \u201cappearance size,\u201d but directly impacts how the entire system integrates.
You may have noticed that pipes labeled DN50 under different standards consistently have a fixed outer diameter of 60.3mm. This is where outer diameter comes into play. Engineering designs, flanges, fittings, and supports are almost always engineered around this outer diameter. If the outer diameter is incorrect, a cascade of problems follows.<\/div>
In practical applications, outer diameter and wall thickness are inseparable. When the outer diameter is fixed, changing the wall thickness alters the inner diameter. Any change in inner diameter affects flow rate, velocity, and pressure drop. Therefore, selecting pipes often requires considering not just \u201chow thick\u201d they are, but how the outer diameter and wall thickness are matched.<\/div>
At PANDAPIPE, we frequently encounter clients who initially specify only \u201cI need DN40.\u201d Before production begins, we must confirm: Where will it be used? What pressure rating is required? What medium will it transport? Will it involve more welding or quick-connect fittings? These conditions directly influence the appropriate outer diameter and wall thickness selection.<\/div><\/article>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Outer Diameter of Steel Pipe Standard Specification Chart<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Steel Pipe Outer Diameter Chart (OD MM, Inch)<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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The unit for tube outer diameter is millimeters or inches<\/strong><\/span>. In the steel pipe outer diameter chart below, you can clearly see the unit conversions between pipe outer diameter, DN, and NPS<\/a>.<\/strong><\/span><\/p>

For example, DN15=NPS 1\/2″=Outer Diameter 21.3 mm=0.84 inch<\/span><\/strong><\/p>

Steel Pipe Outer Diameter Chart<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Nominal Size (DN)<\/b><\/strong><\/p><\/td>

NPS (Inch)<\/b><\/strong><\/p><\/td>

Outer Diameter (mm)<\/b><\/strong><\/p><\/td>

Outer Diameter (inch)<\/b><\/strong><\/p><\/td><\/tr>

DN15<\/p><\/td>

1\/2″<\/p><\/td>

21.3 mm<\/p><\/td>

0.84 in<\/p><\/td><\/tr>

DN20<\/p><\/td>

3\/4″<\/p><\/td>

26.9 mm<\/p><\/td>

1.05 in<\/p><\/td><\/tr>

DN25<\/p><\/td>

1″<\/p><\/td>

33.7 mm<\/p><\/td>

1.33 in<\/p><\/td><\/tr>

DN32<\/p><\/td>

1 1\/4″<\/p><\/td>

42.4 mm<\/p><\/td>

1.67 in<\/p><\/td><\/tr>

DN40<\/p><\/td>

1 1\/2″<\/p><\/td>

48.3 mm<\/p><\/td>

1.90 in<\/p><\/td><\/tr>

DN50<\/p><\/td>

2″<\/p><\/td>

60.3 mm<\/p><\/td>

2.38 in<\/p><\/td><\/tr>

DN65<\/p><\/td>

2 1\/2″<\/p><\/td>

76.1 mm<\/p><\/td>

3.00 in<\/p><\/td><\/tr>

DN80<\/p><\/td>

3″<\/p><\/td>

88.9 mm<\/p><\/td>

3.50 in<\/p><\/td><\/tr>

DN100<\/p><\/td>

4″<\/p><\/td>

114.3 mm<\/p><\/td>

4.50 in<\/p><\/td><\/tr>

DN125<\/p><\/td>

5″<\/p><\/td>

141.3 mm<\/p><\/td>

5.56 in<\/p><\/td><\/tr>

DN150<\/p><\/td>

6″<\/p><\/td>

168.3 mm<\/p><\/td>

6.63 in<\/p><\/td><\/tr>

DN200<\/p><\/td>

8″<\/p><\/td>

219.1 mm<\/p><\/td>

8.63 in<\/p><\/td><\/tr>

DN250<\/p><\/td>

10″<\/p><\/td>

273.0 mm<\/p><\/td>

10.75 in<\/p><\/td><\/tr>

DN300<\/p><\/td>

12″<\/p><\/td>

323.9 mm<\/p><\/td>

12.75 in<\/p><\/td><\/tr>

DN350<\/p><\/td>

14″<\/p><\/td>

355.6 mm<\/p><\/td>

14.00 in<\/p><\/td><\/tr>

DN400<\/p><\/td>

16″<\/p><\/td>

406.4 mm<\/p><\/td>

16.00 in<\/p><\/td><\/tr>

DN450<\/p><\/td>

18″<\/p><\/td>

457.2 mm<\/p><\/td>

18.00 in<\/p><\/td><\/tr>

DN500<\/p><\/td>

20″<\/p><\/td>

508.0 mm<\/p><\/td>

20.00 in<\/p><\/td><\/tr><\/tbody><\/table>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Outer Diameter Formula<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Outer Diameter Formula:<\/span><\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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OD = ID + (2 \u00d7 Wall Thickness)<\/strong><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Click the link below to view detailed information about Nominal Pipe Size (NPS).<\/p>

Nominal Pipe Size \u2013 Size Charts, Calculation Formula<\/a><\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Whether you are a procurement specialist or an engineer, you need to select the correct pipe size.<\/a><\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Common outer diameters have long been standardized, such as:<\/div>
DN15 typically corresponds to 21.3mm;<\/strong><\/span><\/div>
DN20 corresponds to 26.9mm;<\/strong><\/span><\/div>
DN25 is 33.7mm;<\/strong><\/span><\/div>
DN32 is 42.4mm.<\/strong><\/span><\/div>
Moving up:<\/div>
DN40 is 48.3mm,<\/strong><\/span><\/div>
DN50 is 60.3mm,<\/strong><\/span><\/div>
DN65 is 76.1mm,<\/strong><\/span><\/div>
DN80 is 88.9mm.<\/strong><\/span><\/div>
These numbers may seem like static data in a table, but on-site, they are the critical line determining \u201cwhether it will fit.\u201d One wrong choice throws everything off.<\/div><\/article>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Outer and Inner Diameter<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Outer Diameter vs Inner Diameter Chart<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Item<\/th>OD<\/th>ID<\/th><\/tr><\/thead>
Definition<\/td>Outside measurement<\/td>Inside measurement<\/td><\/tr>
Usage<\/td>Pipe selection<\/td>Flow calculation<\/td><\/tr>
Fixed or Variable<\/td>Usually fixed<\/td>Changes with wall thickness<\/td><\/tr><\/tbody><\/table>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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How Does Out Diameter Affect Pipe Performance<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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Outer diameter directly impacts performance. A larger outer diameter, at the same wall thickness<\/strong><\/span>, provides greater structural stability and higher pressure resistance. However, it also consumes more material, increases costs, and may complicate installation. Thus, bigger isn’t always better\u2014the optimal solution is \u201cjust right.\u201d<\/div>
Flow dynamics follow the same principle. A suitable wall thickness paired with the outer diameter determines the inner diameter. A well-chosen inner diameter ensures smooth fluid flow, minimizes pressure drop, and enhances system energy efficiency. Selecting an incorrect outer diameter makes it difficult to achieve optimal performance, even with carefully selected wall thickness.<\/div><\/article>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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How to Select the Outer Diameter\/ Diameter Outside of Steel Pipes
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