Determining the size of PVC pipe can be frustrating and challenging, especially if you're not familiar with how PVC pipes are sized.
FORMUFIT PVC fittings and accessories are available in six (6) PVC sizes that work with both FORMUFIT Furniture Pipe and most off-the-shelf plumbing-grade PVC pipe. However, if you're not sure what size PVC pipe you need, or have, there are a few important things to keep in mind:
- 1. The outside diameter (OD) is not the PVC pipe size. The OD is the measurement of the pipe from the outside edge to the outside edge. The PVC pipe size is actually the inside diameter (ID), which is the measurement of the pipe from the inside edge to the inside edge.
- 2. PVC schedule is important. PVC schedule refers to the thickness of the pipe wall. The higher the schedule number, the thicker the pipe wall and the stronger the pipe.
- 3. Not all PVC pipe is compatible. Some PVC pipe is designed for specific applications, such as water or sewer lines. Make sure you choose the right type of PVC pipe for your project.
- 4, There are four easy ways to determine PVC pipe size. You can measure the OD of the pipe, read the size markings on the pipe, consult a PVC pipe sizing chart, or contact a plumbing professional.
1. The OD is not the PVC pipe size.
PVC pipe sizes are named using the Nominal Pipe Size (NPS) system. NPS is a dimensionless term that approximately relates to the pipe's inside diameter (ID). This means that the ID of a 3/4" size PVC pipe is approximately 3/4 inches, the ID of a 1" pipe is approximately 1 inch, and so on.
It is essential to understand that the PVC pipe size does not refer to the pipe's outside diameter (OD). The OD of a PVC pipe is always larger than the pipe size name due to the additional thickness of the pipe walls. For example, the OD of a 3/4" size PVC pipe is approximately 1.050 inches, and the OD of a 1" size PVC pipe is approximately 1.315 inches.
This is why it is essential to measure the ID of the pipe, not the OD when determining the size of a PVC pipe. You can measure the ID of the pipe using a measuring tape or a micrometer. If you only have the OD of the pipe, you can use our PVC pipe sizing chart (below) to determine the PVC pipe size.
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 unless going off of a reference chart. If you measure the outside diameter of your PVC pipe and order based on that measurement, you will almost always receive the next PVC size up. Never order PVC products based off the outside diameter, unless referencing our PVC pipe dimensions page.
2. PVC Schedule is Important.
PVC schedule refers to the thickness of the pipe wall. The most common schedule is 40, but schedule 80 PVC is also available. As the schedule number increases, the pipe wall gets thicker and the inside diameter of the pipe gets smaller.
FORMUFIT internal-fit products are only compatible with Schedule 40 PVC pipe. This is because the inner diameter of 80 schedule PVC is much smaller than PVC schedule 40, and the inner diameter of Thinwall PVC is too large.
All external-fit products will fit almost all schedules, including Thinwall, Schedule 40, Schedule 80, and even Schedule 120 PVC. This is because the outside diameter of all these schedules is the same and external-fit products go over the PVC pipe.
All off-the-shelf plumbing-grade PVC pipe is marked with the pipe schedule. This is so you can easily identify the schedule of the pipe before you buy it. Please see our PVC Pipe Markings Page to learn how to read them.
PVC Schedule, Visualized.
As the PVC Schedule number increases, the pipe wall gets thicker, which in turn makes the inside diameter smaller. This image indicates what FORMUFIT products are compatible with each Schedule of PVC pipe.
3. 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, made from CPVC and uses an entirely different sizing system. If you use a 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, and sometimes have a stripe that runs down the pipe. For more information on CPVC, please see our CPVC Incompatibilities page here.
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.