PVC 101 - Learn the Basics.

Understanding PVC Pipe Sizes

The size of PVC can, to some, be a very confusing thing. Just like with other building supplies such as lumber, PVC pipe is not true to its actual outside dimensions and is a 'given name only', which can often confuse and frustrate those who wish to build with PVC.

It doesn’t, however, have to be that way. With a quick explanation, you can be quite knowledgeable about PVC is about 5 minutes. Read on to learn more, then check out the FORMUFIT PVC Size Guide as well as the PVC Pipe Size Chart below for additional information on PVC pipe dimensions.

Outside Diameter (a) The PVC pipe Outside Diameter is the distance of the outside of the pipe from one side to the other. If you were to put your forefinger on the top of the pipe and your thumb on the bottom, the distance between your thumb and forefinger would be the PVC Outside Diameter. This is always larger than the actual ‘size’ of the PVC pipe. Inside Diameter (b) PVC pipe Inside Diameter is the distance of the INSIDE of the pipe from one side to the other, also known as the PVC bore. This is what actual PVC pipe ‘sizes’ are based upon. Schedule (c) The schedule of a PVC pipe is the thickness of the pipe wall, all the way around. This will affect the inside diameter of the PVC pipe as the thicker the wall gets, the smaller the interior hole can become. Each PVC pipe has a Schedule number, and is marked on the outside of plumbing-grade PVC pipe. Schedule 40 and 80 are available at most hardware stores and home centers. Schedule 40 pipe is the most common used in structural PVC applications.

PVC Pipe Size Chart

One of the common misconceptions about PVC pipe is that the size of the fitting or pipe that it is ‘titled’ as is the actual outside diameter.  In reality, the actual outside diameter is often LARGER than the pipe or fittings ‘titled’ size.  This is due to the face that PVC sizes are 'in name only', and just names assigned to a size.

For instance, a 1-1/4” pipe is actually 1-5/8”, or 1.660”.  This is due to something called Nominal Pipe Size, or NPS standardization.  This can often confuse the layman when ordering PVC pipe or fittings.  The chart, shown below, outlines the PVC Pipe Size and their actual dimensions in both decimal and fraction.

For instance, you want to build a structure using pipe you’ve purchased from your local hardware store of home center.  Performing a measurement of the outside diameter of the pipe tells you that the pipe outside diameter is approximately 1-5/16”.  Normal thinking would tell us that the logical choice would be 1-1/4” PVC fittings, however, in actuality; the fitting size needed is 1”, as shown in the chart above.

How to Read PVC Pipe Markings

Because plumbing-grade PVC pipe is required to meet certain standards, each pipe is marked by the manufacturer with required information, however, you only need to pay attention to two items in particular (in bold, below):

1. The manufacturer's name or trademark (Charlottle, JM Eagle, etc.)
2. The standard to which it conforms (ASTM, etc.)
3. Material designation (e.g., PVC 12454, of PVC 1120, or PVC Type 1, Grade 1).
4. DWV (Drainage, Waste, Vent)
5. Pressure rating if for pressure (320 PSI, etc.)
6. The Pipe size (usually printed as 1.25" for 1-1/4", .75 for 3/4", etc.).
7. Schedule number (SCHEDULE 40, etc.)

If you need a specific fitting, and you’re not sure how to determine the exterior dimension of the pipe you’re using, you can read the markings on the pipe (plumbing-grade pipe only) to determine its size and schedule.  The two highlighted areas on the example markings below show the pipe size (1.25 or 1-1/4”) in (a) and the Schedule (SCHEDULE40) as (b).  This tells you that your pipe is a 1-1/4” Schedule 40 PVC pipe.

Have additional questions about PVC?  Send us your concerns at questions@formufit.com