Here at eeziflo-fittings we pride ourselves on supplying premium quality pvc pressure pipe systems and pvc pipe fittings at competitive prices, supported by excellent stocks and customer service. We have an extensive range of PVC pipe system components to choose from, including pipe, fittings, valves and accessories. All of our products can be used in a wide variety of applications, from simple garden water features to substantial projects in a variety of sectors. All of our products are classed as PVC pressure pipe fittings (plastic pressure pipe fittings) and are to WRAS standards.


Whilst there are many different worldwide standards governing the size of the finished product, our PVC pressure pipe products are generally available in the two most common standards used in the UK, these being Metric and Imperial sizes. The outside diameter of the pipe per size remains constant, irrespective of the measurement system and it is the bore which changes depending on the wall thickness or pressure rating. But what does this mean? What are the differences between them both?


Both Perform the Same Function

In terms of joining methods, robustness and chemical resistance – both Imperial and Metric pressure pipe systems are exactly the same. There are no differences at all in functionality and performance as it is the same PVC raw material used for both. The variance is not in the composition of the material, but in the size designation and manufacturing standards.


Difference in Pipe Size

Metric also referred to as millimetres (mm) and Imperial also referred to as inch (“) are, of course, both systems of measurement. The Metric system is the most recent, making use of measurements such as millimetres, centimetres and metres etc. This system is commonly used in Europe and is becoming increasingly popular in the UK. Sizes are always referred to using the outside diameter (O.D) of the pipe, e.g. 20mm OD PVC PN16 = 20mm OD x 17mm ID (1.5mm w.t).

The Imperial system is much older, and is well established in the UK and the USA. This system uses measurements such as inches, feet and yards. Sizes are always referred to using the nominal bore (N.B) of the pipe. The Imperial system of size referencing uses nonspecific dimensioning to differentiate between sizes. This originates from historical steel pipe sizes.

There is no correlation between the size reference of the pipe and the actual physical dimension of the pipe, e.g. 1/2” N.B* PVC Class E = 21.4mm OD x 18mm ID* (1.7mm w.t) * 1/2” N.B* = 12.5mm.

As is demonstrated above, there is no correlation between the referenced dimension of half inch (12.5mm) and the actual dimension of the pipe (18mm).

Whilst both systems can be interchanged utilising a range of adaptor fittings such as our Inch/Metric Adaptor Socket and Inch/Metric Adaptor Union it is not common practise to mix the two.


Threaded Fittings Fit Both

Threaded fittings can actually work in metric and imperial pressure pipe systems because they are essentially the same and are always supplied referenced Imperial/Inch i.e there is no such thing as a Metric/mm threaded fitting in the pipework systems that we supply, enabling you to adapt from one system to another with ease.


Imperial vs Metric Pipe Sizes

Have a glance at our Imperial to Metric approx. size comparison chart below.


Always Obtain Professional Advice

If you wish to know more then why not seek professional advice from a team of experienced experts? It is always better to be safe rather than sorry. If you are still unsure whether you have the right system in place, or require some simple advice on your measurement requirements, give us a call today. Alternatively, you can reach us on our contact page or email us directly on