Table of contents
Part 2 of our "Converting units" guide series is all about converting hose dimensions. Corrugated tubing, flexible garden hoses or robust metal conduits: Due to the wide range of hoses, the respective external dimensions of the hoses also vary considerably. Another factor is the purpose for which a hose is intended. Does it need to withstand high water pressure, be heat-resistant or particularly flexible?
Depending on these factors, hoses with the same internal diameter often differ in their external dimensions. It is not for nothing that these differences can lead to a bad purchase.
But don't worry: with the following tips and a hose table for converting an inch hose into a metric measurement, such as mm, you can find the exact matching parts with little effort.
What sizes are there for a hose?
The inner diameter of a hose is usually specified in inches or using the designation DN (Diameter Nominal), as specified in the EN ISO 6708 standard, among others.
This measurement, which is commonly used for garden hoses, also indicates the approximate inner diameter of the hose. Depending on the manufacturer and hose variant, the abbreviation OD (Outside Diameter) also indicates the outer diameter of the hose. Information on the wall thickness is also not uncommon. In the case of pre-assembled hoses, the length of the hose is often specified in addition to the outside and inside diameter.
What are the sizes of the outer diameter of a hose and how can it be calculated?
The outer diameter of a hose is calculated using the following simple formula:
Outer diameter = inner diameter + 2 x wall thickness
Note: We recommend using a calliper gauge to determine the wall thickness and inside diameter if the hose does not have any measurements. As the wall thickness of a hose can vary depending on the manufacturer, intended use and material, the outer diameters of the respective hoses also differ considerably. For example, manufacturers such as FLEXA offer hoses and corrugate tubes with different outer diameters (OD), ranging from 2.3 to 95 mm depending on the hose variant.
Other important hose parameters
The inner hose diameter is the most important parameter to ensure that hose nozzles or connector for corrugated tubing connectors fit flush into a hose and that a watertight and airtight connection between hose and nozzle is guaranteed. The overall, outer diameter of a hose is also decisive, depending on the intended use. For example, if the hose is pulled through a wall opening or has to fit into an empty conduit that has already been laid or into a supply shaft.
Important when selecting suitable hose lines: The nominal diameter (internal diameter) of a hose is also specified in DN (Diameter Nominal) in accordance with DIN EN ISO 6708. The DN dimension is usually printed on the hose.
How can the nominal diameter DN be calculated using the outside diameter and the wall thickness?
DN (Diameter Nominal) can be calculated using the following formula as an analogue parameter to the inside diameter:
DN/inner diameter = outer diameter - 2 x wall thickness
According to DIN 8062, e.g. for plastic pressure pipes made of PVC-U, the inner diameter (DN) is usually given in mm. According to the British system, however, the inside diameter (DN) of pipes and hoses is expressed in inches.
How to measure inch threads and hoses correctly
The easiest way to measure a hose is to determine its inside diameter. Ideally, this should be done with a caliper gauge. Based on the internal dimension, it is then easy to find a suitable end nozzle, for example. It is helpful in this context that hose connections are usually defined by two technical data.
- by the outer diameter of the hose nozzle for the respective hose
- by the sizes of the inch thread of the hose connection
Note: An avoidable measuring error in this context is to only measure the outer diameter of the hose, as the inner diameter can vary depending on the wall thickness of the hose. However, if the wall thickness is unknown, it can also be easily calculated if the outer and inner diameters of the hose are known.
How do you calculate the wall thickness of any hose?
Wall thickness = (outer diameter - inner diameter) / 2
To avoid making the wrong purchase, the hose diameter should always be determined in mm beforehand. Contrary to what you might think, a hose nozzle with a Withworth G 2 inch outer pipe thread, for example, has an outer diameter of 59.16 mm, which is larger than the inch size would suggest.
The inner diameter of a 2 inch hose, on the other hand, is significantly smaller at approx. 50 mm (2 x 2.54 cm). The problem with this is that the G 2 inch hose nozzle does not fit the 2 inch hose, meaning that neither a force-fit nor a watertight connection is possible.
Convert common hose dimensions from inches to mm
As already mentioned, the outer diameter of a hose depends on its wall thickness. When determining the wall thickness, any manufacturer and measurement tolerances must also be taken into account.
It makes sense to determine the hose dimension in mm, e.g. to determine the right hose nozzle. However, hose dimensions are usually sold in inches. This also applies to the hose diameter, which is usually given in inches instead of a metric measurement such as mm. In our guide Converting inches to mm, we explain how you can generally convert customs units into both mm and cm.
Common hose sizes include the following hose sizes in inches, as well as their metric equivalent in centimetres or mm.
| Hose sizes in inches | Hose inner diameter in mm |
|---|---|
| 1/8" | 3.2 |
| 1/4" | 6.3 |
| 3/8" | 9.5 |
| 1/2" | 12.7 |
| 5/8" | 15.9 |
| 3/4" | 19 |
| 1" | 25.4 |
| 1 1/4" | 31.8 |
| 1 1/2" | 38.1 |
| 2" | 50.8 |
| 2 1/2" | 63.5 |
| 3" | 76.2 |
| 4" | 101.6 |
| 5" | 127 |
| 6" | 152.4 |
| 8" | 203.2 |
| 10" | 254 |
Download table
What is the inner diameter (DN) for inch hoses?
We have summarised the DN in mm and inches for common hoses in the following table.
| Hose diameter in inches | Hose diameter in mm |
|---|---|
| 1/8" | 3.18 |
| 1/4" | 6.35 |
| 3/8" | 9.53 |
| 1/2" | 12.7 |
| 5/8" | 15.88 |
| 3/4" | 19.05 |
| 1" | 25.4 |
| 1 1/4" | 31.75 |
| 1 1/2" | 38.1 |
| 2" | 50.8 |
| 2 1/2" | 63.5 |
| 3" | 76.2 |
| 4" | 101.6 |
| 5" | 127 |
| 6" | 152.4 |
| 8" | 203.2 |
| 10" | 254 |
Download table
The question often arises in the gardening sector, for example: What is the diameter of a one-inch hose? This actually trivial question is not so easy to answer.
Despite careful editing and checking of the content, Stecker Express assumes no liability for the topicality, correctness, completeness and quality of the information provided.
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