How to Avoid Common Pipe Measurement Mistakes

DIY-ers unfamiliar with plumbing tend to order the wrong sized pipe. Sound familiar? If so, take a few minutes to look through this guide, learn a little about measuring pipes, and you can save yourself a lot of frustration on your next pool plumbing project.

So What’s the Confusion?

Pipe sizes have something called nominal sizes, which is the North American set of standard sizes. This causes trouble for people because the nominal size of the pipe is a measurement of the inside of the pipe.

So if you’re buying a two-inch pipe, those two inches only count the diameter of space within the pipe. It doesn’t take the pipe’s walls into account.

Measuring PVC Piping

With PVC piping you need to measure the internal diameter, which will match the nominal size.

To use this chart, first measure the pipe’s outer diameter, find the corresponding measurement on the chart, and it will tell you the pipe’s internal diameter as well. This gives you a more complete picture about the pipe’s size.

Measuring Pipe Thread Size

Starting with a male pipe thread, measure the outer diameter of the pipe and then subtract one-quarter inch.

Subtracting a quarter inch accounts for the pipe walls which are each one-eighth of an inch thick.

For a female pipe thread you can measure the internal diameter to determine what pipe to pair it with.

With threaded pipe you should also pay attention to the threads per inch. You’ll notice that multiple pipe sizes share the same amount of threads per inch. It’s good to be aware of this so you can avoid any confusion between sizes.

What’s the Difference Between Male and Female Pipe Thread?

Not sure whether you’re dealing with male or female pipe thread?

It does matter which gender you’re dealing with. When it comes to the trades, “anything that sticks out is male and anything that goes in is female--especially if two things fit together whereby one has features that stick out and the other has features that go in,” Carlos Mano explains in this eHow article. “If a tab fits into a slot, the tab is male, and the slot is female. The part of a plug that is inserted into another plug is male, and the plug it is inserted into is female. When two threaded pipes fit together, the one that is threaded on the outside is male, and the one that is threaded on the inside is female,” he explains.

Measuring Lengths

There are also some conventions to be aware of when you’re measuring the length of pipes. Check out the video above, which demonstrates these pipe measurement terms:

Measuring end to end. This means you are measuring the length from one end of the pipe to the other end.

Measuring end to center. This term means that you are measuring from the end of the pipe and ending the measurement at the centre of the attached fitting.

Measuring center to center. You can probably guess this one, it’s for measuring a pipe with a fitting at each end. Measure from the center of one fitting and end the measurement at the centre of the fitting on the opposite end.

Now that you know the basics and language used when dealing with pipe measurements you can be confident in ordering pipes for your pool’s plumbing. However, if you still have any questions feel free to contact the customer service team at Pool Supplies Canada. We’re happy to help!