Wednesday, November 6, 2013

The Skinny on Pipe Sizes

Dear sir,
I see that water treatment systems come with different size pipe connectors, such as ¾”, 1”, 1-1/4” etc.  I have no idea what size our pipes are, how do I find that out? Do I measure the outside diameter of the pipe?  I plan to install a whole house water filtration system to filter chlorine and sediment from our tap water.
Indianapolis, IN

Good question.  Pipe measurements can be tricky, as their sizes don't always correspond to their exact dimensions.
As a brief historical aside: This is because when pipe sizes were standardized by the American Standards Association back in 1927 there were only 3 wall thicknesses in wide use, so a system of schedule numbers was created to delineate half-steps between these 3 thicknesses, which obviously didn't fit all applications.  Over time these schedule numbers began to deviate from the wall thickness sizes they were meant to represent, but the system stuck.

The measurements you're referring to (¾”, 1", etc.) are called nominal sizes, and don't necessarily reflect the pipe's inside or outside diameter.
Think of a 2x4: even if it isn't 2' x 4' we still call it a 2x4 - the same goes for pipe sizes.  

Pictured: Pipes!
Knowing the size of your pipes is crucial to selecting a water treatment system that will work with your well and plumbing system, and luckily it's very easy to find out. 
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

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

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

We hope this helps, Bob.  And we hope you'll seek us out again once you've figured out your pipe sizes and are ready to select a water filtration system - we're available for any assistance you might need selecting, installing, or operating your systems. Just e-mail us at or drop us a line on Facebook
Thanks for the letter!