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The majority of hot tub pipe used by the UK hot tub industry is based on a North American set of standard pipe sizes. However, be aware if your spa is Asian origin you will need to ring us to discuss pipe sizes further.

Hot tub piping is sized according to "Nominal Pipe Size" (NPS); it is based on the nominal size of the pipe (in inches) and a 'Schedule'

The schedule specifies the wall thickness of the pipe, according to the NPS, Hot tub pipe is Schedule 40.

To ascertain your pipework size:

Measure the outer diameter of the pipe. The table below shows the outside diameter of schedule 40 pipe, as used in hot tubs:

NPS
 Outside Diameter
 3/8 inch
(14 mm)
 1/2 inch
(21.5 mm)
 3/4 inch
(28 mm)
1 inch
 1.315 inch (33.40 mm)
1-1/4 inch 1.660 in (42.16 mm)
1-1/2 inch
 1.900 in (48.26 mm)
2 inch
 2.375 in (60.33 mm)
2-1/2 inch
2.875 in (73.02 mm)
3 inch
3.500 in (88.90 mm)