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How to measure the size of your water pipes

When installing a new treatment system in your home, it’s very important to measure your pipe sizes. Many problems can be easily avoided by ensuring that the size of the system piping matches the size of your incoming piping. This is largely to eliminate problems associated with blocking water flow and pressure buildup.

 pipe sizeKnowing your pipes’ sizes is crucial to selecting or installing the right plumbing system and water treatment system for your well. 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.

The reason for this – for those interested – is that when pipe sizes were standardized by the American Standards Association (ASA, now known as ANSI) 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.

Check first to see if the piping is labeled with the size. Many piping systems in homes are labeled with their sizes where visible. Often though, it can be tricky to spot. When there’s no label on the pipes, you can measure the circumference of the pipe and then converting to the units used in pipe sizing. You can use either a 1) a piece of string about 6 inches long, or 2) a tape measure.

pipe sizeRemove any insulation that may be around the pipe. Then, wrap the string around the circumference of the pipe one time. Remove it from the pipe and measure the length of the circumference to the nearest 1/8”. Look up in the tables below for the corresponding pipe size according to the type of pipe it is.

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″ pipe

Flexible (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.

pipe size - copper pipes


 Any further questions about making sure you are ordering the correct system for your home? Contact us at or at the phone number at the bottom of this webpage. You may also contact us on Facebook. We are happy to help.

pipe size


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  • Clean Water Systems & Stores, Inc., Water Treatment Equipment,Service & Supplies, Santa Cruz, CA

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