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PVC 101 - Finding Your PVC Pipe Size

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.  

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:

  1. The Outside Diameter is not the PVC Pipe Size.
  2. PVC Schedule is Important
  3. 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 ‚Äėwalls‚Äô 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 ‚Äėbore‚Äô 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.

Additional Ways to Find PVC Pipe Size

If you need to find out a PVC pipe size, do one of the following:

Get Our PVC Size Guide

Download PVC Size Guide

You can download our PVC Size Guide, which is a print-to-scale solution that will allow you to physically compare your PVC pipe to each PVC Pipe Size specifications.

Read the Pipe Markings

Read Pipe Markings

If you use plumbing-grade PVC pipe for your projects, you can read the pipe markings. Every plumbing-grade manufacturer marks their pipes differently, however you can view our Reading PVC Pipe Markings page to learn how to read them.

Compare to Other Objects

PVC Size Comparison

The outside diameter of PVC pipes have are similar in size to some common household objects. You can view our Pipe Size Comparison chart, which will give you an idea of how each PVC Pipe Size diameter equates to regular household objects.

Measure the Physical Pipe

PVC Size Dimensions

Measure the outide and inside diameter of your PVC pipe, and compare it to our PVC Pipe Dimensions chart to translate it into the correct PVC Pipe size. You can view our PVC Pipe Dimensions chart and look at all of the detailed information on the pipe sizes.

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:


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.

ABS Pipe

While ABS pipe is size-compatible with most FORMUFIT products, it cannot be cemented together using standard PVC cement.  A special transitional cement must be used, or the pipe to fitting connection must be screwed together to connect them securely.  ABS pipe is also very brittle and is not recommended for structural use.

Steel Conduit or Pipe

Steel pipe and conduit have the same outside diameters as the corresponding PVC pipe sizes and are size-compatible, but are not recommended for use with PVC joints & fittings, as there is no way to connect the steel pipe to the plastic PVC fitting.  In most cases the steel pipe will easily slide out of the fitting, resulting in loose, or possibly collapsing, structures.