Hot Tub Plumbing Pipe Sizes Explained

Choosing the correct pipe size can be confusing

Help Article ID36A


At Hydrospares we realise that when it comes to choosing the correct pipe or fittings needed for your requirements, it can sometimes become a little confusing, especially when it comes to selecting the correct plumbing size. This Help Article is here to help you avoid the common mistakes made by so many when selecting the pipe & fitting size they need. 

 

 Hot Tub Plumbing Pipe Sizes Explained

Step 1

 

The first step is to measure your actual pipe's OD (Outside diameter) in mm. Using a set of Vernier’s is normally the quickest and most accurate way.

 

Helpful Tip

If you do not have access to a set of Verniers take a sheet of paper and wrap it around the pipe, mark where the paper overlaps. Straighten out and measure the distance in mm, this will now give you the pipe's circumference.  Divide this by 3.14 which will provide you the pipe's diameter.



Its important to measure accurately, the difference between the metric and imperial pipe sizes only differ by a few mm. 

Its also important to ensure you measure the actual pipe not the pipe fittings this can be difficult sometimes due to fittings being glued up against each other.

 
 
 

 

Step 2 

Now you know your actual pipe OD (outside Diameter) you can select the correct pipe size. Use the charts bellow work out the size needed based off your actual pipes OD (outside diameter) in mm. Match your measurement with one of the figures in the outer column (Actual Outside Dia. mm)

 

METRIC PLUMBING 

If you are replacing a Metric size pipe the diameter should match exactly. Common metric sizes are 20mm, 32mm, 40mm, 50mm, 63mm, 75mm

Note - Metric plumbing is not that common in domestic hot tubs and is more often used in Pools and commercial spas.
 
 
METRIC PIPE

REFTYPE

ACTUAL
OUTSIDE DIA. MM

    20mm         METRIC     20mm
32mmMETRIC32mm
40mmMERTIC40mm
50mmMETRIC50mm
63mmMERTIC63mm
75mmMETRIC

75mm

 

IMPERIAL PLUMBING 

If you are replacing Imperial sized pipe this is where it gets a little confusing. imperial sizes are based on the bore of the pipe and their sizes have no direct correlation to their OD (Outside Diameter)
  
Note - Imperial pipes are most commonly used in domestic hot tubs & Pools
 
 
IMPERIAL PIPE

REFTYPE

ACTUAL
OUTSIDE DIA. MM

    3/8 Inch         IMPERIAL     14mm
1/2 InchIMPERIAL21.5mm
3/4 InchIMPERIAL28mm
1 InchIMPERIAL33.4mm
1-1/4 InchIMPERIAL42.16mm
1-1/2 InchIMPERIAL

48.26mm

2 InchIMPERIAL

60.33mm

2-1/2 InchIMPERIAL

73mm

3 InchIMPERIAL

88.9mm

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Schedule / Class 

 
Pipes manufactured in the USA will go by a schedule whereas European manufactured pipe have a class rating. Both are just a set of standards for the pipes pressure rating which will have an effect on the wall thickness of the pipe. without effecting the OD. The thicker the wall the higher the pressure rating.  In most domestic hot tub or pool settings the pressures used are well below the entry level of pressure ratings for PVC pipe. Full information and ratings will be visible on our site within the product page.