Poly Pipe Sizing Guide: How to Choose the Right Size for Your Project in Malaysia

How Poly Pipe Sizes Are Measured

Before we jump into the size chart, there’s one critical point to understand: PE pipe is measured by its outside diameter (OD), not the inside.

This is different from how traditional galvanised iron (GI) pipes are measured (which use nominal bore/inside diameter). It’s a common source of confusion, and getting it wrong during ordering can mean your fittings won’t match your pipe.

For example, a 25mm PE pipe has an outside diameter of 25mm. After subtracting the wall thickness (which depends on the pressure class), the actual internal diameter is smaller – typically around 20mm to 21mm for a PN10 rated pipe.

This is why two pipes labelled “25mm” can deliver different flow rates – their wall thickness (and therefore internal bore) may differ depending on the pressure rating.

Here’s the quick conversion between PE pipe metric sizes and their imperial equivalents, since many Malaysian plumbers still reference pipe sizes in inches:

Source: Parsethylene Kish

Complete Poly Pipe Size Chart (PE100, PN10)

Below is the detailed sizing chart for the most commonly used PE pipe specification in Malaysia – PE100 material at PN10 pressure rating (SDR 17). This covers the sizes you’ll find stocked at most reputable hardware suppliers, including NY Hardware.

Source: Engineering Toolbox (ISO 4427)

Which Size Do You Need? A Practical Breakdown

Theory is one thing. Knowing what size works for your actual project – that’s where it counts. Here’s a real-world guide based on common applications in Malaysia:

25mm Poly Pipe – The Residential Standard

The 25mm size is the workhorse for Malaysian homes. It’s the standard size for service connections – the pipe that runs from the water meter at your gate to the main inlet of your house.

Best for: single-storey and double-storey homes, small offices, and individual retail units. A 25mm PN10 pipe delivers adequate flow for up to 2–3 bathrooms running simultaneously under normal municipal water pressure.

32mm PE Pipe – The Upgrade Option

If you’re building a house with more than 3 bathrooms, have a rooftop tank that needs filling, or simply want better pressure on upper floors, 32mm is the smart upgrade. The jump from 25mm to 32mm increases the internal cross-sectional area by roughly 78% – meaning significantly more water can flow through at the same pressure.

Best for: larger homes, semi-D and bungalow properties, small commercial units.

50mm PE Pipe – Commercial & Multi-Unit

When a single 25mm or 32mm line can’t keep up, 50mm steps in. This size is commonly specified for shophouse rows, small apartment blocks, and commercial buildings where the water demand from multiple outlets is high.

According to the US Fusion technical guide, medium-diameter pipes in the 50mm to 110mm range are ideal for commercial and municipal distribution networks where consistent flow rates are critical.

110mm – 200mm – Municipal & Infrastructure

These are the sizes you’ll see in housing development trunk lines, factory water supply mains, and municipal distribution networks. In Malaysia, the national Pipe Replacement Programme is replacing 1,844km of aging pipes – and HDPE in these diameter ranges is the preferred replacement material due to its leak-free fused joints.

Common Sizing Mistakes to Avoid

Over the years at NY Hardware, we’ve seen the same sizing mistakes come up again and again. Here are the top three – and how to avoid them:

1. Confusing OD with ID

As we explained above, PE pipe uses outside diameter while GI pipe uses nominal bore (inside diameter). A “1-inch GI pipe” has a different flow capacity than a “32mm PE pipe” even though they’re considered equivalent. Always check with your supplier to ensure your fittings and connections match.

2. Undersizing to Save Cost

Going one size smaller might save you a few ringgit per metre. But if your system can’t deliver enough flow, the cost of ripping up and replacing buried pipes will far exceed those savings. This is especially common in Malaysian properties that later add a water heater, additional bathroom, or irrigation system – all of which increase demand beyond the original design.

3. Ignoring Pressure Loss Over Distance

Water pressure drops the further it travels through a pipe. For long runs (over 30 metres), you may need to go one size up to compensate for friction loss. This is particularly relevant for rural Malaysian properties or farms where the water source is far from the point of use.

Conclusion

Choosing the right pipe size doesn’t have to be complicated – but it does need to be deliberate. The size chart above gives you the technical dimensions, and the practical breakdown shows you which sizes work for which applications.

The golden rule: when in doubt, go one size up. The cost difference is marginal, and you’ll thank yourself later when your system handles future demand without breaking a sweat.

If you’re still unsure which size is right for your project, our team at NY Hardware has been advising contractors and homeowners on pipe sizing for over 10 years. Get in touch with us, and we’ll help you spec the right pipe – no guesswork involved.

For a deeper look at HDPE pipe specifications and pressure ratings, read our detailed guide on HDPE PN10 Pipe: Sizes, Specs & What You Need to Know. Or if you’re weighing up different pipe materials entirely, our PVC vs Poly Pipe comparison breaks down the pros and cons of each.

Browse our full range of PE pipes at NY Hardware →