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Determining what size PVC pipe you are using in your project or that you picked up from the home center can be a frustrating and challenging process. FORMUFIT products are available in six (6) PVC sizes that work with FORMUFIT PVC pipe, but also work with off-the-shelf plumbing grade PVC pipe, available from your home center or hardware store. You can use PVC pipe machine to produce PVC pipe.

If you have not worked with PVC pipe before, or are not familiar with how PVC pipes are sized, we highly recommend you review the following three important details about PVC Pipe sizing:

The Outside Diameter is not the PVC Pipe Size.

PVC Schedule is Important

Some Pipe isn’t Compatible

The Outside Diameter of the pipe is not the PVC Pipe Size.
PVC Pipe sizes are so named by the measurement of the inside diameter (also called the bore) of the PVC pipe, and not the outside diameter. If you measure the outside diameter it will give you a larger reading than the actual PVC Pipe Size. The pipe will always be larger on the outside than the size name, as the thickness of the ‘walls’ of the pipe make it larger.

Correct way to Measure
FORMUFIT products follow the Nominal Pipe Size (NPS) naming convention or PVC specifications, which identifies the diameter of the hole of a PVC pipe with a closely-related dimensional number for its size. Therefore the Pipe Size for all of our products is based on the inside hole or ‘bore’ of the PVC pipe that it fits. This is the correct way to measure what PVC Pipe Size you need.

Incorrect way to Measure
You should never use the outside diameter of the pipe to determine your PVC pipe size. If you measure the outside diameter of your PVC pipe and order based off that measurement you will almost always receive the next PVC Size up. Never order PVC products based off the outside diameter.

Important: PVC Schedule
PVC Schedule (abbrev. SCH or Sch.) is the thickness of the PVC pipe wall. The most common Schedule is 40, but Schedule 80 PVC is also available. As the schedule gets larger the pipe wall gets thicker from the outside in, so the inside hole (bore) of the pipe gets smaller.

FORMUFIT internal-fit products, such as Internal Dome Caps, Adjustable Elbows and Internal Couplings are only compatible with Schedule 40 PVC pipe. All FORMUFIT Furniture Grade PVC pipe is Schedule 40. Our internal-fit products will not work with PVC Schedule 80, as the inner diameter of 80 Schedule PVC is much smaller than PVC Schedule 40.

All off-the-shelf pressurized plumbing-grade PVC pipe is marked with the pipe schedule. Please see our PVC Pipe Markings Page to learn how to read them.

Some Pipe isn’t Compatible
Not all types of pipe will work with FORMUFIT fittings and accessories:

CTS/CPVC Pipe
The most commonly confused non-compatible pipe is Copper Tube Size (CTS) plastic pipe, which is actually made from CPVC and uses an entirely different sizing system. If you use CTS pipe with FORMUFIT fittings or accessories they will be much too large for the pipe. CTS and CPVC can be identified by their yellowish or tan color, and are marked in the manufacturer printings as CTS or CPVC. For more information on CPVC, please see our CPVC Incompatibilities page here.
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