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Whether for engineers or learners, understanding pipeline systems inevitably involves understanding their specifications. Among these, size is one of the most basic and most important parameters.
When we talk about the size of a pipe, we might simply think it refers to its diameter. But in fact, it’s not that simple. This is because there are many different types of pipes — with different materials, purposes, wall thicknesses, and so on — which means we can’t describe their size in a one-size-fits-all way.
This post will explain the relevant knowledge about pipe size, such as how size is expressed, units used, conversion tables, and more.
Ways to Express Pipe Size
There are various ways to express pipe size. We often see these letters and symbols: “DN”,”OD”, “ID”, “NPS”, “Φ”. All of these can be used to indicate pipe size, but there are some differences between them. Sonraki, I’ll explain them to you one by one.
Nominal Diameter
It is abbreviated as “DN”. Many people mistakenly believe that it refers to the actual diameter of the pipe, but this is a misunderstanding. Nominal diameter is not the actual or standard diameter, nor is it the outer or inner diameter. It is actually a commonly used naming standard for pipe sizes in Europe and Asia. Since there are many types of pipes and fittings—such as various connectors, valves, flanges, and so on—a unified size standard is needed to define them clearly. That’s what nominal diameter is. You can think of it as an industry convention for referring to pipe size.
Outside Diameter and Inside Diameter
Outside Diameter is abbreviated as “OD”, and Inside Diameter is abbreviated as “ID”. Comparing them side by side makes them easier to understand. The concepts of outer diameter and inner diameter exist because pipes have wall thickness, and when we calculate pipe dimensions precisely, wall thickness must never be ignored.
The outside diameter is the diameter of the outermost edge of the pipe, and the inside diameter is the outside diameter minus the wall thickness. As shown in the diagram below, L1 is the outside diameter, L2 is the inside diameter, and L3 is the wall thickness. The relationship between them can be expressed with the formula: L1 = L2 + L3 × 2.
Örneğin, if the outside diameter of the pipe is 50mm and the wall thickness is 2mm, then its inside diameter would be 50 – 2 × 2 = 46mm.
Nominal Pipe Size
It is abbreviated as “NPS”. Similar to DN, it is also an industry-standard name for pipe size, rather than referring to a specific outer diameter or inner diameter. Fakat, it is commonly used in the American standard system (ASME/ANSI).
Φ
This symbol generally refers to the outside diameter of a pipe. Since the pipes we commonly use are round, their outside diameter can be represented by “Φ”.
Örneğin, if we see “Φ100”, it means the pipe’s outside diameter is 100 millimeters. If we see “Φ100×4”, it means the outside diameter is 100mm and the wall thickness is 4mm.
Units of Pipe Size
The units of pipe size are generally divided into metric units and imperial units. For metric units, the most commonly used unit internationally is millimeter (mm). For imperial units, the most commonly used unit internationally is inch (inch/”). The conversion between them is: 1 inch = 25.4 mm.
In general, DN uses millimeters as the unit, while NPS uses inches as the unit.
To give an example, if we see DN80, it means the nominal diameter of the pipe is 80 millimeters. But please note, this number does not mean that the actual outer or inner diameter of the pipe is exactly 80 millimeters.
If we see NPS 3″, it means the nominal pipe size is 3 inches. But again, please note, this number does not mean that the actual outer or inner diameter of the pipe is exactly 3 inches.
Pipe Size Conversion Table
The concepts of outside diameter and inside diameter are easy to distinguish. But for DN and NPS, some people may still have difficulty fully understanding them. So, to help deepen your understanding, I’ve created a comparison table of DN, NPS, OD, and ID. By referring to the table below, you can better understand the relationships between them and how to convert between them.
Please note that the inside diameters listed in the table are approximate values. This is because pipes vary in wall thickness and type — for example, PE pipes, PVC pipes, steel pipes, vesaire. — and their wall thicknesses and standards are different. Öyleyse, for convenience, I’ve used approximate values in the table. If you need detailed data, feel free to bize Ulaşın.
| Pipe Size Conversion Table (DN, NPS, OD, ID) | |||
| Nominal Diameter(mm) | Nominal Pipe Size(“) | Outside Diameter(mm) | Approximate Inside Diameter(mm) |
| 15mm | 1/2″ | 21.25mm | 15mm |
| 20mm | 3/4″ | 26.75mm | 20mm |
| 25mm | 1″ | 33.5mm | 25mm |
| 32mm | 1-1/4″ | 42.25mm | 32mm |
| 40mm | 1-1/2″ | 48mm | 40mm |
| 50mm | 2″ | 60mm | 50mm |
| 65mm | 2-1/2″ | 73mm | 64mm |
| 70mm | 2-1/2″ | 75.5mm | 70mm |
| 80mm | 3″ | 88.5mm | 80mm |
| 100mm | 4″ | 114mm | 106mm |
| 125mm | 5″ | 140mm | 131mm |
| 150mm | 6″ | 165mm | 156mm |
| 200mm | 8″ | 219mm | 207mm |
| 250mm | 10″ | 273mm | 259mm |
| 300mm | 12″ | 325mm | 309mm |
| 350mm | 14″ | 377mm | |
| 400mm | 16″ | 426mm | |
| 450mm | 18″ | 478mm | |
| 500mm | 20″ | 529mm | |
| 600mm | 24″ | 630mm | |
| 700mm | 28″ | 720mm | |
| 800mm | 32″ | 820mm | |
Çözüm
Through this article, you should now have a clear understanding of what “DN”, “OD”, “ID”, “NPS”, Ve “Φ” each mean, as well as their conversion relationships. I hope the content of this article is helpful to everyone.
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Yazar: Michael
Editör: Michael
İçerik Gözden Geçiren: Michael
