Measure Your Supply Pipe Circumference:
Grab a piece of string about 6″(152mm) long. Strip away any insulation so you can get at the pipe and wrap the string around it. Measure how many inches of string it takes to go around the pipe once. This is the circumference of the pipe (yikes, bad memories of high school geometry!). Using the circumference we can calculate the diameter of the pipe. But school’s out so let’s forget about doing geometry calculations! Based on the string length use the table below to find your pipe size.
For Copper or PEX Pipe
- 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
For 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
For Flexible 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
Your string length will probably not be exactly the same as the lengths in the chart. Measurements vary a little, depending on how much the string stretches, dirt on the pipe, manufacturing tolerance of the pipe, how accurate you are at measuring, etc.
Provided free of charge for homeowners and professionals, this tutorial has been continuously refined since 1995 to teach professional irrigation methods. Although the content is optimized for Western U.S.A. environments, its scientific principles are applicable globally. By using this information, the user agrees that no warranties or guarantees are provided, and they assume all responsibility for the suitability of the design for their specific project.