Diameters conversion chart – Hoses and pipes size chart

Diameter Conversion chart - hoses and pipes size chart

Conversion of DN diameters to inches

To convert DN to inches, the following formula can be used:

Inches = DN / 25.4

25.4 is the number of millimetres in one inch.

Suppose we want to convert a diameter of DN 50 into inches. To do this, we do the following operation:

50 / 25,4 ≈ 1,97

The result shows that the diameter of DN 50 is approximately 1.97 inches.

Pipe and hose size chart in different standards

DN [mm] INCH [in] ISO [mm] DIN [mm] METER [mm] DIN 11850 [mm] SMS [mm] ASTM [mm]
6 1/8'’ 10.2         10.29
8 ¼'' 13.5         13.72
10 3/8'’ 17.2 14 12 10   17.15
15 ½'’ 21.3 20 18 18   21.34
20 ¾'’ 26.9 25 23 22   26.67
25 1'' 33.7 30 28 28 25 33.40
32 1 ¼'' 42.4 38 35 34 32 42.16
40 1 ½'’ 48.3 44.5 43 40 38 48.26
50 2'' 60.3 57 54 52 51 60.33
63           63.5  
65 2 ½'’ 76.1 76.1 69 70   73.03
76           76.1  
80 3'' 88.9 88.9 84 85   88.90
  3 ½”           101.6
100 4'' 114.3 108 104 104 101.6 114.3
125 5'' 139.7 133 129 129   141.3
150 6'' 168.3 159 154 154   168.3
200 8'' 219.1 216 204 204   219.1
250 10'' 273 267 254 254   273
300 12'' 323.9 318 304 304   323.9
350 14'' 355.6 368 354 354   355.6
400 16'' 406.4 419       406.4
450 18'' 457.2 459       457.2
500 20'' 508 521       508
  22”           558.8
600 24'' 609.6 622       609.2
  26”           660.4
700 28'' 711.2 720       711.2
  30”           762
800 32'' 812.8 820       812.8
  34”           863.6
900 36'' 914.4 920       914.4
1000 40'' 1016 1020       1016

What is the diameter D?

Diameter D is the outer diameter, a technical term used to describe the outer cross-sectional dimension of a pipe or hose. This is a crucial measurement typically given in millimeters or inches, which is of fundamental importance in selecting components that fit into piping systems, such as connectors, seals, or supports.

In the context of various standards, such as ISO, ASTM, DIN or SMS, the outer diameter is the standard dimension on the basis of which pipes and hoses are classified. This makes it possible to unify them and ensure compatibility in international trade and engineering projects.

The D-diameter is essential for correctly fitting and sealing pressure systems. It also determines the size and type of components needed.

D diameter

What is the diameter DN?

DN is the nominal diameter. "Diameter Nominal"). It acts as a standard nomenclature used to classify pipe sizes in the plumbing and construction industry, as well as in other industries using piping.

The term "nominal" in the context of DN does not refer to the actual dimensions of the pipe diameter, but to a standard designation that simplifies technical communication and design. It is therefore referred to by some as "physically non-existent".

DN is expressed in millimetres and refers to the internal diameter of a pipe in a conventional way, without taking into account the wall thickness.

For example:

A DN20 pipe with a wall thickness of 1.5 mm will have an inner diameter of 22 mm, not 20 mm as DN states.

DN diameter

What is the difference between D and DN diameter?

The difference between D and DN diameter is that the former refers to the actual outer diameter, while the latter is used for identification purposes and does not always directly correspond to the physical dimensions of the pipe.

In practice, engineers and technicians should be familiar with both dimensions in order to properly design piping systems and select the right components.

What is a DIN diameter?

The DIN diameter is a dimension that refers to the standards set by the Deutsches Institut für Normung (German Institute for Standardisation), which is responsible for creating norms and technical standards in Germany. They are widely recognised and used worldwide, especially in Europe.

In the context of pipes and pipe connections, DIN diameters define both the outer and inner dimensions of pipes and their fit. DIN standards often refer to the precise dimensions of pipes, fittings, flanges and other hydraulic components, ensuring that they are manufactured and used in a consistent and interchangeable manner.

DIN diameter

What is an ISO diameter?

ISO diameter is a dimension that refers to a series of international pipe standards defined by the International Organisation for Standardisation (ISO). These standards aim to facilitate global trade and cooperation by ensuring uniformity in the dimensions of products, including pipes and fittings.

For pipes, ISO standards specify dimensions such as outer diameters, inner diameters and wall thicknesses. These are key data for engineers and designers, as they enable the design of piping systems that can be assembled from components manufactured by different companies around the world.

ISO is intended to ensure that pipes of a specific ISO diameter have the same dimensions regardless of where they are manufactured.

ISO diameter

What is a DIN 11850 diameter?

Diameter DIN 11850 is a dimension that refers to a specific set of German standards (Deutsches Institut für Normung) for pipes used primarily in the food and pharmaceutical industries. This standard specifies in detail the dimensions of stainless steel pipes, including their outer diameters, inner diameters and dimensional tolerances and wall thickness.

The DIN 11850 standard is designed to ensure a high level of hygiene and ease of cleaning, which is essential in the food and pharmaceutical industries where pipes must meet stringent sanitary requirements.

DIN 11850 diameter

What is the ASTM diameter?

ASTM diameter is a dimension that refers to pipe standards set by the American Society for Testing and Materials (ASTM), the international organisation that sets technical standards. ASTM develops and publishes a wide range of technical specifications for various materials, products, systems and services, including pipe dimensions.

ASTM diameter standards are relevant to a wide range of industries, including construction, petrochemicals, water and wastewater, and other industrial applications where pipes are a key component of transmission systems.

ASTM pipe outer diameter is often specified in inches and is used in conjunction with other parameters, such as wall thickness and pressure classes, to ensure that pipes and their fittings are accurately sized and fit properly.

What is the SMS diameter?

The SMS diameter is a dimension that refers to a pipe standard defined by the Swedish Manufacturing Standard (SMS), which originated in Sweden. SMS standards are particularly important in the food, pharmaceutical and biotechnology industries, where pipes must meet high hygienic and quality norms.

The SMS standard specifies the exact dimensions of the pipes, including their outer and inner diameters, as well as their wall thickness. In addition, special attention is given to the smoothness of the inner and outer surfaces, which is crucial for applications that require easy cleaning and contamination prevention.

This makes the SMS standards ideal for use in environments where high hygiene is required, such as in the food industry or pharmaceutical production.

What is fi diameter?

Diameter fi is the term used to describe the diameter of a circle, and in the context of pipes and hoses, the outer diameter of these elements.

In practice, diameter fi (denoted by the symbols φ or D) is measured straight through the centre of a pipe from one side to the other. It is a basic dimension used not only in piping structures, but also in many other engineering and manufacturing sectors, such as machinery, equipment or mechanical parts.

Diameter fi is usually expressed in metric units such as millimetres or centimetres, although in some regions (such as the United States) imperial units such as inches may be used.

fi diameter

What is the difference between fi and DN diameter?

The difference between fi and DN diameter is that the former describes the actual outer diameter, while the latter is a conventional measure of the inner diameter that facilitates the identification and classification of pipes, but does not always reflect their exact physical dimensions.

What is SDR?

SDR is the ratio of a pipe's outer diameter to its wall thickness. It is a standard method of pipe classification, most commonly used in the plastics and polymer industries. It allows the pressure resistance of a pipe to be determined.

SDR (Standard Dimension Ratio) is expressed as a number that results from dividing the pipe's outer diameter by its wall thickness. For example:

  • a pipe with an external diameter of 200 mm and a wall thickness of 10 mm has an SDR of 20 (200 mm / 10 mm = 20).

The lower the SDR value, the thicker the pipe wall in relation to its diameter, which usually means higher pressure resistance.

SDR ratio

The Standard Dimension Ratio is an important parameter in the design of piping systems. Especially those that are intended to transfer liquids or gases under pressure. SDR allows pipes to be selected appropriately according to pressure requirements and operating conditions, ensuring the safety and reliability of the installation.

How to read pipe dimensions?

In order to read pipe dimensions, you should distinguish between the basic parameters of the pipe, i.e.:

  • outer diameter (D or fi), 
  • wall thickness, 
  • nominal diameter (DN) or inner diameter (ID).

Suppose we have a pipe designated as:

DN 100, fi 114.3 x 6.02

We can read this as follows:

Pipe with a nominal diameter (DN) of 100 mm, an external diameter of 114.3 mm and a wall thickness of 6.02 mm.

However, take into account that manufacturers and retailers describe pipes in different ways. Unfortunately, there is no single scheme that applies to every shop, but the fi diameter very often appears in the designation. Sometimes, in addition to (or instead of) the wall thickness, it is accompanied by a number indicating the length of the pipe.

How to measure the diameter of a pipe?

To measure the diameter of a pipe, follow the steps below:

  • Select a measuring tool - It is best to use a calliper to measure the diameter, which provides high accuracy. Alternatively, you can reach for slightly less precise solutions such as a ruler or measuring tape.
  • Clean and prepare the pipe - Make sure the surface of the pipe is clean and free of any debris that could interfere with the measurement.
  • Insert the calliper - Place the calliper jaws around the pipe. Then gently tighten them to accurately encompass the outer edge. 
  • Read the value - Read the value on the calliper. 
  • Repeat the measurement - To be sure, take the measurement at several different points along the pipe to check for deviations in diameter.

When measuring the inner diameter of the pipe, use the smaller jaws of the calliper or other tools such as a depth gauge or internal calibre.

How to read hose dimensions?

To read hose dimensions, you should know the same parameters as for pipes, ie:

  • outer diameter, 
  • wall thickness, 
  • inner diameter.

The most common way of describing hose sizes in retail shops is the following formula:

Hose name, inner diameter x outer diameter

For example:

4x8 mm silicone hose

Based on the above description, we can conclude that we are dealing with a hose with an inner diameter of 4 mm and an outer diameter of 8 mm. This would also mean that the wall thickness of the hose is 2 mm, which you calculate from the following formula:

(outer diameter - inner diameter) / 2

However, bear in mind that for hoses the descriptions are not standardised either, so they can vary from manufacturer to manufacturer.

How to measure the diameter of a hose?

To measure the diameter of a hose, follow the steps below:

  1. Select a measuring tool - It is best to use a calliper to measure the diameter of the hose to ensure an accurate reading. 
  2. Measure the outer diameter - Gently place the calliper jaws around the hose, making sure they lie parallel to the surface of the hose. Then read the result.
  3. Measure the inner diameter - If you have access to the end of the hose, insert the smaller calliper jaws into the hose to measure the inner diameter. To do this, stretch them gently and read the result. 
  4. Repeat the measurement - To be sure, measure the diameter in several different places. Hoses may have a different diameter at different sections, especially if they have been used or exposed to harmful environmental factors. 
  5. Pay attention to the hose condition - If the hose is worn or damaged, this can affect the accuracy of the measurement.
Photo of Bartosz Kułakowski - CEO of Hosetech sp. z o. o.

Articles author

Bartosz Kułakowski

CEO of Hosetech Sp. z o.o.

Bartosz Kulakowski is an industrial hoses and couplings specialist with over 10 years of experience. Bartosz has been present in the technical industry since 2013. He gained experience as a technical and commercial advisor in the sector of plastic conveyor belts, steel structures, industrial hoses, and connectors. Since 2016, he has specialized exclusively in hoses and connectors. In 2019 he opened his own business under the HOSETECH Bartosz Kulakowski brand and since July 2022 he has been the CEO of the capital company HOSETECH Sp z o. o. (LLC).

SPIS TREŚCI

Conversion of DN diameters to inches

Pipe and hose size chart in different standards

What is the diameter D?

What is the diameter DN?

What is the difference between D and DN diameter?

What is a DIN diameter?

What is an ISO diameter?

What is a DIN 11850 diameter?

What is the ASTM diameter?

What is the SMS diameter?

What is fi diameter?

What is the difference between fi and DN diameter?

What is SDR?

How to read pipe dimensions?

How to measure the diameter of a pipe?

How to read hose dimensions?

How to measure the diameter of a hose?

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