Skill Builder: An Introduction to PVC Pipe Sizing

PVC pipe is an amazing material. The most obvious use for it is to transport water, but, as anyone who reads Make: regularly knows, it can be made to do many different jobs.

One thing that might not be obvious though is how big a piece of pipe is. They are generally sold in 10′ sections, which are actually 10′ long, but what about the other dimension? That isn’t quite so intuitive.

Nominal Sizes

Although in the United States a pipe might be labeled as, for example, “1 inch,” what does that really mean? You might think it’s the outer diameter, but for 1″ NPS (Nominal Pipe Size) PVC, the OD is actually 1.315 inches. The inner diameter is actually a little closer to this number, but varies between schedule 80 pipe at .935″, and thinner wall Schedule 40 pipe at 1.033″.

Internationally, sizes may be labeled as a “DN” value, or Diameter Nominal, expressed in millimeters.

Where to Get This Information

A quick search online reveals this reference, which has tables for Schedule 40 PVC pipe as well as Schedule 80. For a reference trusted by engineers and tradespeople for over 100 years, The Machinery’s Handbook is a great resource, and these figures can be found under “Plastic Pipe” on page 2,532 of my 27^th edition. Use the index in back if you have another edition!*

Different Types of Pipe

Although Schedule 40 PVC is what you will most commonly see at a hardware store, some projects call for a different material. Schedule 80 PVC is stronger and heavier than Schedule 40, but still maintains the same outer diameter. If you need something even stronger and “more” metallic, steel pipe maintains the same outer dimensions as PVC for each nominal size, and have several wall thicknesses to choose from.

Non-Traditional Pipe Uses

Although transporting water is still an excellent use for pipe, Make: is full of uses that were never thought of by its original creators. One of my favorites, is this PVC “pipe organ.” As I made it, I’m a little biased, but searching a little further reveals that you can, for example, make home furnishings of this material. There’s even a technique to stain it in a new color if you want.

*At least one figure obtained by subtracting 2 times wall thickness minus OD per Machinery’s Handbook 27 page 2,532 slightly disagrees with the linked figure above. Observed ODs are consistent between sources.