Hot Tub Plumbing Pipe Sizes Explained

Choosing the correct pipe size can be confusing

Help Article ID

36A

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.

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
REF	TYPE	ACTUAL OUTSIDE DIA. MM
20mm	METRIC	20mm
32mm	METRIC	32mm
40mm	MERTIC	40mm
50mm	METRIC	50mm
63mm	MERTIC	63mm
75mm	METRIC	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
REF	TYPE	ACTUAL OUTSIDE DIA. MM
3/8 Inch	IMPERIAL	14mm
1/2 Inch	IMPERIAL	21.5mm
3/4 Inch	IMPERIAL	28mm
1 Inch	IMPERIAL	33.4mm
1-1/4 Inch	IMPERIAL	42.16mm
1-1/2 Inch	IMPERIAL	48.26mm
2 Inch	IMPERIAL	60.33mm
2-1/2 Inch	IMPERIAL	73mm
3 Inch	IMPERIAL	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.