Pool & Spa plumbing sizes and names can be confusing, as plumbing sizes are referred to as "Nominal" sizes. "Nominal" means "by name only" and does not reflect the actual dimensions of the pipe. This is because pipes were originally measured by the internal diameter, where they slipped over a fitting. With time, the wall thickness became more important, and the name stuck or evolved. 

Important Measuring Information:

  • For Pipe Sizes, measurements are always taken from the Outside Diameter (OD) of the Pipe itself, OR the Inside Diameter (ID) of the Socket of a fitting.
  • For Pipe Classes, meausrements are taken from the Internal Diameter of the pipe.
  • The OD of a fitting or socket is completely irrelevent, as the thickness of fittings varies widely.

Below are some charts with names over the actual dimensions. In Pool & Spa water plumbing, for spas and pools, generally we only use "Pressure Pipe," not DWV or other plumbing sizes.

PVC Pressure Pipe ASNZ 1477 Dimensions¹:

Imperial Metric Outside Diameter Class 9 IDº Class 12 IDº Class 18 IDº
1/2" 15mm ~ 21.2-21.5mm 18.3mm 17.8mm
3/4" 20mm ~ 26.6-26.9mm 23.7mm 22.4mm
1" 25mm ~ 33.4-33.7mm 30.5mm 29.8mm 28.1mm
32mm ~ 42.1-42.4mm 38.5mm 37.5mm 35.4mm
1.5" 40mm ~ 48.1-48.4mm 45.2mm 44.1mm 42.8mm
2" 50mm ~ 60.2-60.5mm 55.2mm 53.7mm 50.5mm
65mm ~ 75.2-75.5mm 68.9mm 67.0mm 63.2mm
2.5" ~ 73mm
  • º Some pipe manufactures may have different Internal Dimensions
  • ¹ Not all pool or spa fittings are exactly these measurements, as they do not necessarily adhere to Australian Standards. Chinese spas will sometimes have completely proprietary fittings.

Hose & Tube Dimensions

Imperial Metric Inside Diameter
3/8" 9-10mm 9mm
3/4" 19mm 19mm