Sep. 05, 2025
Cross-linked polyethylene, or PEX, has revolutionised the plumbing industry in Australia. Its flexibility, durability, and resistance to scale and chlorine make it a superior choice for many residential and commercial applications. However, for anyone embarking on a plumbing project, understanding PEX pipe sizes is crucial for ensuring adequate water pressure and flow. This comprehensive guide will break down the standard PEX pipe sizes used in Australia and help you select the right one for your job.
Understanding PEX Size Measurements: Metric vs. Imperial
One of the first points of confusion in Australia is the mix of measurement systems. While Australia officially uses the metric system, plumbing components often reference imperial sizes due to historical influences and international manufacturing standards.
PEX pipe sizes are typically denoted in two ways:
Imperial (Inches): The most common reference, e.g., 1/2", 3/4".
Metric (Millimetres): The outside diameter (OD) in mm, e.g., 12mm, 20mm.
It's critical to understand that the imperial size (e.g., 1/2") refers to the nominal diameter, which is roughly the inner diameter. The actual outside diameter will be larger.
Standard PEX Pipe Sizes in Australia
The most commonly available and used PEX pipe sizes in the Australian market are:
Note: 1/2" PEX can sometimes have an OD of 12mm or 15mm. Always check the manufacturer's specifications and ensure your fittings match the OD exactly.*
Which PEX Pipe Size Should You Choose?
Selecting the correct size is a balance between ensuring sufficient flow rate and maintaining good water pressure.
1. 1/2 inch PEX (12mm/15mm OD)
Applications: This is the most common size for fixture supply lines. It's perfect for supplying water to individual points of use.
Best For: Running lines to sinks, toilets, vanities, washing machine taps, and other branch lines. It's flexible and easy to manoeuvre through wall cavities.
2. 3/4 inch PEX (20mm OD)
Applications: This is the standard size for main water supply lines and manifold trunks.
Best For: The main line running from your water meter or pump to the house, and from the manifold to various sections of your home. Using 3/4" pipe for main runs ensures you don't experience a significant pressure drop when multiple fixtures are used simultaneously (e.g., someone showering while the washing machine is running).
3. 1 inch PEX (25mm OD)
Applications: Used for high-flow demand applications and as the primary inlet for large manifolds.
Best For: Large homes with multiple bathrooms, commercial properties, or long pipe runs from the water source to the dwelling. It's also common for underground service lines between the meter and the house.
Key Considerations for Australian Projects
Local Regulations: Always check with your local council or a licensed plumber regarding the specific standards and regulations in your area. In Australia, plumbing work is highly regulated, and most water supply work must be performed by a licensed professional.
Manifold Systems: PEX is ideally suited for home-run (or manifold) plumbing systems. This involves running a dedicated 1/2" line from a central manifold to each fixture. This design maintains consistent pressure and allows you to shut off water to individual fixtures without affecting others.
Pressure Ratings: PEX pipe in Australia is commonly available in PN12 (12 bar pressure rating) for potable water, which is more than sufficient for standard residential water pressure (typically 500 kPa or ~72 psi).
Quality and Standards: Look for PEX pipes that are certified to AS/NZS 4020 (for testing of products for use in contact with drinking water) and marked with the WaterMark logo, a mandatory certification for plumbing products in Australia.
FAQ: PEX Pipe Sizes Australia
Q: Can I use 1/2" PEX for my main water line?
A: While possible in very small dwellings, it is not recommended. A 3/4" line is standard for mains to ensure adequate flow and pressure to all fixtures.
Q: Are PEX fittings the same size as the pipe?
A: Fittings are designed to match the outside diameter (OD) of the pipe. A 1/2" fitting is for a pipe with a ½" nominal size but a specific OD (e.g., 15mm). You must match the fitting to the pipe's OD, not just the nominal size.
Q: Can I connect PEX to existing copper pipe?
A: Yes, absolutely. Transition fittings are readily available to connect PEX to standard threaded or soldered copper fittings (e.g., 1/2" PEX to 1/2" copper).
Conclusion
Choosing the right PEX pipe size is fundamental to the success and efficiency of your plumbing system. For most Australian homes, a combination of 3/4 inch (20mm) for main trunk lines and 1/2 inch (15mm) for branch lines is the ideal setup. Always prioritise quality products with the WaterMark certification and, when in doubt, consult a licensed plumber to ensure your system is safe, efficient, and compliant with all Australian standards.
