Measuring poly pipe diameter isn't a one-size-fits-all approach; it depends crucially on the type of poly pipe you're dealing with.
The key distinction lies between rural/low-density poly pipe and metric poly pipe, as each type uses a different standard for specifying its size.
Understanding Poly Pipe Measurement Standards
Based on industry practices and common conventions:
- Low density and rural poly pipe are typically measured and referred to by their inside diameter (ID). This is the diameter of the hole through which water or other fluids flow.
- Metric poly pipe (often used for mains water, irrigation, and other pressure applications) is measured and referred to by its outside diameter (OD). This is the total width of the pipe, including the wall thickness.
Knowing whether the measurement refers to the inside or outside diameter is vital for selecting the correct fittings and ensuring compatibility within a plumbing or irrigation system.
Practical Examples
Let's look at specific examples to illustrate this difference:
| Pipe Type | Stated Size | Measurement Basis | Approx. Inside Diameter (ID) | Approx. Outside Diameter (OD) |
|---|---|---|---|---|
| Rural Poly Pipe | 1 inch | Inside Diameter | 24mm | 29mm |
| Metric Poly Pipe | 25mm | Outside Diameter | 20mm | 25mm |
- As shown, a 1" rural poly pipe has an inside diameter of approximately 24mm, but its outside diameter is 29mm. When you buy "1 inch rural pipe," you are referring to the nominal inside size.
- Conversely, a 25mm metric pipe has an outside diameter of exactly 25mm, but its inside diameter is around 20mm (depending on the pressure rating or wall thickness, e.g., PN12.5 as in the reference). When you buy "25mm metric pipe," you are referring to the nominal outside size.
Therefore, to accurately measure and identify poly pipe diameter, you first need to determine if the pipe is rural/low density or metric, and then measure accordingly using calipers or a tape measure across the relevant diameter (inside for rural/low density, outside for metric).
