The size of the Flex or Rigid PVC pipe in your pool or hot tub is identified using the inside diameter measurement of the pipe - this measurement is known as 'Nominal', which means a referenced name. One of the issues that is commonly encountered when trying to measure pipe size in a hot tub is that the outside diameter of the pipe is often measured and incorrectly provided, which actually gives you a completely different (and larger) PVC pipe dimension then what you may actually require.

If you are going to measure the outside diameter of the pipe, do the following:

• Take your outside diameter measurement, and then refer to the tables below for the Actual Outside Diameter
• Once you find the actual outside diameter of the pipe in the chart, then look at the Pipe Size beside it - this will be the nominal pipe size, and tell you the size of fittings you want to be ordering

Actual Outside Diameter

The measurement of the pipe from top to bottom, or left to right. Taken from the outside edges of the pipe section.

This measurement is not your PVC pipe size.

Inside Diameter

The measurement of the pipe from top to bottom, or left to right. Taken from the inside opening of the pipe section.

This measurement is equal to your PVC pipe size.

Pipe Wall Thickness

The measurement of the thickness of the PVC pipe. Taken from the outside to the inside of the pipe section.

This measurement changes for each Schedule of PVC piping.

PVC Schedule 40 Pipe and Flex Pipe Sizing Table

Schedule 40 PVC pipe and flex pipe is compatible with all external-fit and internal-fit fittings for pools and hot tubs.

PVC Schedule 80 Pipe

Schedule 80 PVC pipe is only compatible with external-fit fittings. Internal-fit fittings, such as Internal Dome Caps, Adjustable Elbows, Internal Couplings and other fittings that fit inside of the PVC pipe will not work with SCH 80 PVC due to the smaller internal diameter.

PVC Thinwall Pipe

Thinwall PVC pipe is only compatible with external-fit fittings. Internal-fit fittings, such as Internal Dome Caps, Adjustable Elbows, Internal Couplings and other fittings that fit inside of the PVC pipe will not work with Thinwall PVC due to the larger inner diameter.

CPVC Pipe

CPVC pipe, also known as Copper Tube Size (or CTS) plastic pipe commonly sold at home improvement centres uses a different system for measurement, and is not compatible with any standard PVC fittings from the pool and spa industry.