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 or International 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 |
BSP - British Standard Pipe Thread Sizes:
|
BSP Thread Size |
Outside Diameter mm / inch |
TPI |
|---|---|---|
|
1/16 Inch BSP |
7.7 mm / 0.304" |
28 |
|
1/8 Inch BSP |
9.7 mm / 0.383" |
28 |
|
1/4 Inch BSP |
13.16 mm / 0.518" |
19 |
|
3/8 Inch BSP |
16.66 mm / 0.656" |
19 |
|
1/2 Inch BSP / 15mm |
20.99 mm / 0.825" |
14 |
|
5/8 Inch BSP |
22.99 mm / 0.902" |
14 |
|
3/4 Inch BSP / 20mm |
26.44 mm / 1.041" |
14 |
|
7/8 Inch BSP |
30.20 mm / 1.189" |
14 |
|
1 Inch BSP / 25mm |
33.25 mm / 1.309" |
11 |
|
1-1/4 Inch BSP |
41.91 mm / 1.650" |
11 |
|
1-1/2 Inch BSP / 40mm |
47.80 mm / 1.882" |
11 |
|
2 Inch BSP / 50mm |
59.61 mm / 2.347" |
11 |
|
2-1/4 Inch BSP |
65.71 mm / 2.587" |
11 |
|
2-1/2 Inch BSP |
75.18 mm / 2.96" |
11 |
|
3 Inch BSP |
87.88 mm / 3.46" |
11 |
|
4 Inch BSP |
113.03 mm / 4.45" |
11 |
|
5 Inch BSP |
138.43 mm / 5.45" |
11 |
|
6 Inch BSP |
163.83 mm / 6.45" |
11 |
