Categories: Installing Water Treatment SystemsPipesTutorial

Pipe Sizes

Knowing your pipes’ sizes is crucial to selecting or installing the right water treatment system for your well and plumbing system. Unfortunately, the sea of pipe sizes can be a bit tricky to navigate, due to the fact that pipe sizes don’t actually reflect their true dimensions.

ASA is now known as ANSI

The reason for this – for those interested – is that when pipe sizes were standardized by the American Standards Association back in 1927 there were only 3 wall thicknesses in wide use.

These 3 thicknesses obviously didn’t fit all applications, so a system of schedule numbers was created to delineate half-steps between these 3 thicknesses. Over time these schedule numbers began to deviate from the wall thickness sizes they were meant to represent, but the system stuck.

Nowadays, we refer to pipes by their nominal sizes – 3/4″, 1″, etc. While generally close in measurement, these sizes don’t necessarily reflect either the inside or outside diameter of the pipe.

Luckily, finding the size of your pipes isn’t very hard at all:

If you haven’t already, check the pipes themselves: often their size will be labeled on the side. If so, your work is done.

If not, try the string method. This simply entails removing any insulation from your pipe, wrapping a string around it, and marking off the length of string needed to encircle the pipe once. Then, just measure this length of the string with a ruler, and you’ve got your pipe’s circumference. Now that you know its circumference, use the tables below to find its size.

Copper Pipe or PEX tubing
2.75″ (70mm) = 3/4″ pipe
3.53″ (90mm) = 1″ pipe
4.32″ (110mm) = 1 1/4″ pipe
5.10″ (130mm) = 1 1/2″ pipe

Steel Pipe or PVC Plastic Pipe
3.25″ (83mm) = 3/4″ pipe
4.00″(102mm) = 1″ pipe
5.00″(127mm) = 1 1/4″ pipe
6.00″(152mm) = 1 1/2″ pipeFlexible (usually black) Polyethylene Pipe
2.96-3.33″ (75-85mm) = 3/4″ pipe
3.74-4.24″ (95-108mm) = 1″ pipe
4.90-5.57″ (124-141mm) = 1 1/4″ pipe
5.70-6.28″ (145-160mm) = 1 1/2″ pipe

Once you’ve figured out your pipes’ sizes, you’re ready to start looking into a water treatment system. You can browse our selection of high-quality treatment and purification systems in our online store, and read our free how-to guides for more information on selecting, installing, and operating our systems.

For further questions or comments, e-mail us at support@cleanwaterstore.com or contact us on Facebook. Thanks for reading!

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Gerry Bulfin

Gerry Bulfin is the founder and owner of Clean Water Systems & Stores, Inc. (Clean Water Store) in Santa Cruz, California, which he started in 1986. He is a WQA Master Water Specialist, WQA Certified Installer, California Grade II Water Treatment Operator, and California Licensed Contractor (C-55 Water Conditioning), CSLB #1003944. Gerry is a long-time member of the Water Quality Association (WQA), the National Ground Water Association (NGWA) and the American Water Works Association (AWWA), and shares practical, test-based advice on choosing, installing and maintaining well and city water treatment systems.