Irrigation Pipe Sizes & Measurements: Here’s How They Differ in Australia

Understanding irrigation pipe sizes and measurements is essential when you are working with PVC pipes. Every PVC pipe is measured in different ways using different metrics, and knowing how to understand these measurements is essential in finding and using the right sized pipes.

Irrigation systems are used everywhere, from residential and commercial gardens, backyards, golf courses, and farms among others. Given the broad and many uses of irrigation pipes, it would be beneficial to learn more about their specificities. Regardless of use, whether you’re a plumber, builder, irrigator, or even an auto mechanic speak a similar language. When you’re referring to measurements and sizes, PVC pipes are measured in imperial and metric measurements. 

Irrigation pipes are measured based on their diameter, thickness and the thickness of the pipe wall. This information is used to connect PVC pipes to other compatible pipes, and ensure the thickness of the pipe is suitable for your application. 

In this article, we will specifically be tackling the sizing of irrigation pipes, how they are measured, and how their measurements affect the performance and output of irrigation systems. Continue reading if you want to learn more.

Are Irrigation Pipes Measured in Imperial or Metric?

Irrigation pipes are measured in both imperial and metric measurements. Here in Australia, we almost always use the metric system for things like lengths of pipe, but the standardised measurements for pipe thicknesses and diameters still use the imperial system. 

While confusing, it is an unfortunate fact that many measurement and sizing terms are spoken in both Imperial and Metric due to the age and type of the industry.

Sometimes Imperial and Metric can be heard in the same sentence, ie: “I need a 6m length of ¾ inch PVC”. Therefore, a level head and quick thinking is required to understand and convert Imperial to Metric and vice versa.

The Metric system of units, which is the most common in Australia, uses metres and kilograms with decimal places that reference a value of 1,10,100,1000 etc.

The Imperial system of Measurement is unofficially also used in Australia as this was the common unit of measurement until a large-scale conversion was completed in 1974. Common Imperial measurements are inches & feet and ounces & pounds with relevant fractions that do not have decimal places. ie: ¼ inch, 6 foot 3/8 inch.

To make matters more confusing, some plumbing and irrigation pipe and fitting sizes are not even the same as what they are called.

Why Is Pipe Size Important In irrigation?

Understanding which pipe sizes to use is critical as this affects both flow rate and water pressure. Pipes, regardless of the type, inherently have rough internal surfaces. The internal surface of these pipes cause friction to the flowing water, which reduces the water pressure. 

This is known in some parts of the world as “burning” the water pressure. The loss in water pressure due to friction is formally known as ‘head-loss’.

With this in mind, you’d understand that since water has to travel faster in smaller pipes, more water pressure is lost to friction. Decreased water pressure is bad if you have long pipelines which end in sprinklers in your irrigation system — you need a certain amount of water pressure to keep the sprinklers working as intended. 

If your irrigation system utilises a number of sprinklers, or any other irrigation device that requires an ample amount of pressure, then it would be wiser to use larger pipes to maintain or minimise the loss of pressure. Alternatively, you may need to choose sprinklers for low water pressure or consider a pressure booster pump. 

It is important to remember that although changing pipe size, whether larger or smaller, may seem like it would only provide a marginal increase or decrease in water pressure, it results in something much more substantial. For instance, increasing the pipe’s diameter from 63mm to 75mm might seem like just a couple notches larger, the 20% diameter increase actually equates to a 45% increase in the cross sectional area of the pipe. So changing pipe sizes provides an exponential change, not a linear one. If you’re in the market to replace an old pipe, you need not bother with the old size. Instead, find out the flow rate requirement by identifying the pipe’s purpose.

Remember, flow rate and pressure are different, though they are related and impact one another. 

What Is The Standard Irrigation Pipe Size?

There is no universal or “one size fits all” pipe size for irrigation systems in Australia. There is however, standardised pipe sizings based on provisions set forth by what is known as AS/NZS — joint Australian and New Zealand Standards, which are approved and published by the Council of Standards Australia. 

Different variations of pipes, particularly to what material they are constructed from, conform to different AS/NSZ standards. For instance, the standard sizing for poly pipes are based on the AS/NZS 4130:2018, while PVC pipe sizes are based on the AS/NZS 1477.

PVC Pipe Sizes in Australia

PVC pipe and PVC fittings are not defined by their internal diameter or even their external diameter, which can be very confusing and frustrating, especially for first-time users.

25mm or 1 inch pressure PVC pipe (in this case, class 12), has an internal diameter of 30mm. The external diameter of the pipe is 34mm.

20mm or ¾ inch pressure PVC pipe (in this case, class 12), has an internal diameter of 23mm with an external diameter of 27mm. Therefore, it can be quite difficult when people guess or try to measure the pipe size and are convinced that they need a 25mm pipe (because they measured it!) when in reality, they need a 20mm pipe. Fittings can lead people astray even more because a coupling for 25mm PVC pipe is actually measured as 40mm!

Poly Pipe Sizes in Australia

There are two primary types of poly pipes in Australia — metric and rural. Metric MDPE (Medium Density Polyethylene) pipes are actually measured based on their Outside Diameter (OD), while Rural Pipes are measured based on their Internal Diameter (ID).

High Density Polyethylene pipes or HDPE pipes are another standardised metric poly pipe thickness. MDPE metric poly pipes and metric poly fittings  are larger and thicker pipes that are not only used for industrial liquid transfer such as in large scale agricultural settings, but are also used to transfer gas. This poly pipe rating is found universally around the world. 

HDPE Pipe Size Chart (AS/NSZ 4130:2009)

Rural poly pipes and rural poly fittings are a staple in the agricultural industry, and are found commonly due to their resilient build quality, and the fact that they can be laid out easily across any type of terrain without bending, twisting or kinking; and providing a constant, unrestricted flow of water. 

Rural poly pipes and fittings can still be found today in a variety of agricultural settings. Many farmers choose to buy rural poly pipes because of how flexible and tough it is, as you’re able to get years out of it without any signs of wear or deterioration. 

Rural Poly Pipe/MDPE Size Chart

Rural poly pipe sizes are one of the most common sizes of irrigation pipe thicknesses. MDPE pipes, or medium density polyethylene pipes share the same pipe sizing chart as rural poly pipes.

LDPE Poly Pipe Size Chart

LDPE or low density polyethylene pipes are another thickness of poly pipe commonly found in irrigation and agriculture. LDPE pipes and LDPE fittings use their own size scaling chart as they are significantly smaller than other standardised pipes and fittings.

BSP Pipe Sizes

British Standard Pipe, or BSP thread, is a standard screw thread that has been adopted Internationally, including Australia; similar to the NPT thread, which is the US standardised classification for irrigation pipes that have a tapered threaded end offering another way to provide watertight seals between PVC pipes. 

BSP threads are also measured differently, as a 25mm thread size may actually have a diameter of 32mm. It is imperative, then, that all fitting and pipe sizes are not based on their actual dimensions.

BSP Thread Sizes

How Do I Know What Size Irrigation Pipe I Need?

The best way to know what size irrigation pipe you need is to use the markings found on existing pipes to purchase the same type and thickness from your irrigation supplier. Failing that, bringing a sample piece will allow you to match existing pipes with those available in store.

Knowing your current tap flow rate will also be beneficial when choosing PVC pipe sizes. Every irrigation system has a different flow rate which will not only affect the piping you choose, but will actually affect your plants. Flow rate will affect the size and thickness of the pipes that you use, the way you water your plants and how effectively those plants will grow. Without accurate flow and pressure measurements, you could waste time and money installing pipes that are inefficient or incompatible with your tap flow rate.

It is also worth mentioning that not all material has the exact same thread size and pitch. Brass, PVC, LDPE, Nylon, Stainless Steel, Gal, Aluminium and other pipe or pipe fitting materials may all have minor variations and may therefore not have a perfect screw fit. Always use some form of thread sealant when binding threaded fittings, such as thread sealant tape for poly pipe or pipe thread sealant for PVC pipe.

And don’t forget the old adage – measure twice, cut once.

What Size PVC Pipe is Used For Irrigation?

One of the most commonly used sizes of PVC pipe for irrigation systems are 13mm, 19mm, and 25mm. For irrigation laterals, PVC pipes that are at least ¾” thick (19.05mm) are preferred since those that are ½” thick (12.7mm) clog much faster and often.

What Size Pipe Should I Use For Drip Irrigation?

For most types of drip irrigation systems, 13mm and 4mm poly pipes would suffice. However, this depends on the type of drip irrigation system you plan to, or are currently using. 

These drip irrigation systems may use specific drip emitter types, such as clean/ precision drippers, or variable flow drippers and tricklers. Although there are brand-specific/ proprietary drip irrigation systems, 13mm and 4mm pipes are often still adequate enough.

How Does Pipe Size Affect Flow Rate?

In pipelines in which water flows, the pipe’s size directly affects both water pressure and the flow rate. For fluids (such as water) passing through pipes, any reduction to the pipes’ diameters will compress the fluid — this makes it flow faster, hence, increasing the flow rate. 

Consequently, any increase in the diameter will likewise reduce the flow rate. Water pressure also affects flow rate, as they are directly proportional to each other. An increase in water pressure results in an increase in flow rate, which is why it’s important to learn how to measure your tap flow rate. 

So, if you’re only just setting up an irrigation system and trying to figure out how to choose the right sprinkler set-up, the total flow rate achieved by your pipes will determine how much sprinklers, or other irrigation devices you can use/ your pipelines can supply. With this in mind, it is best to plan your irrigation system accordingly. Identify your desired irrigation output, and from there, work your way down to the kind of pipes, their pressure ratings, as well as their sizes. 

Does Reducing Pipe Size Increase Pressure?

Yes, because in pipelines, water pressure and pipe size are inherently dependent on each other. Any decrease in the diameter will equate to an increase in the water pressure. 

This relationship is scientifically explained in what is known as Bernoulli’s Theorem, in which pressure can be reduced if the area of conveyance is reduced. A smaller pipe will put more resistance to the flow, which increases water pressure. Consequently, a larger pipe decreases such resistance and will correspond to a decrease in water pressure.

Another factor in water pressure is the pipe’s length. Longer pipes offer less resistance to flow and therefore results in a loss in water pressure. This effect is reversed when using shorter pipes, which provide much more resistance to flow, which is part of the constant relationship between flow rate and water pressure. 

Related Questions

What Is The Flow Rate of a 25mm Pipe?

The flow rate of a 25mm Class 12 PVC Pressure Pipe is at 23 Litres Per Minute (LPM) at 20 metres of friction loss, or 18 LPM at 30 metres of friction loss.

The potential flow rates are reduced by friction loss that occurs in the connected pipe work. Although such losses can be minimised by connecting vertical drop pipes to larger horizontal pipes, some degree of friction loss will always be present. Keep in mind that different kinds of pipes also offer varying capacities — 25mm Class 12 pipes have 38% more capacity than 25mm poly pipes.

What Is The Outside Diameter of 1 Inch Poly Pipe?

A 1 inch poly pipe (which refers to its nominal pipe size) has an Outside Diameter (OD) of 1.315” or 33.4mm, this is based on the (American Society for Testing and Materials) ASTM D3035 standard specification of Poly pipes (PE pipes). 

However, based on Australian Standards, particularly AS/NZS 4130:2009 alongside guidelines set forth by the Plastics Industry Pipe Association of Australia (PIPA), the nearest Australian equivalent to a 1 inch pipe is a pipe with an OD of 32mm.

Is PVC Pipe Diameter Inside or Outside?

In Australia, PVC pipe diameters are measured in accordance with the standard specification AS/NZS 1477:2017, which measures both the Outside Diameter (OD) and the DN, or the Nominal Diameter. 

This means that pipe sizes can be determined by their DN or OD, since they are standardised. However, the same sized pipes can have different Internal Diameters (ID) which determine their pressure ratings (PN6, PN9, PN12, etc.).

Is Poly Pipe Measured ID or OD?

Poly pipes in Australia are measured using their Outside Diameter (OD) as standardised by the AS/NZS 4130:2009 in conjunction with guidelines from the Plastics Industry Pipe Association of Australia (PIPA).

What Do the Markings on PVC Pipe Mean?

The markings on PVC pipe tell you the DN number and the PN class of the pipe. The DN number is used to tell you the size of your PVC pipe and the PN class tells you the thickness of the pipe walls. This information is used to ensure your PVC pipes are compatible with each other, and how much pressure they can handle. 

Disclaimer:

This article is published for general informational purposes only and does not constitute professional advice. Any action you take upon the information you find on this website is strictly at your own risk. Always ensure you have the right qualifications and certifications to carry out DIY work and never put your safety at risk. Hills Irrigation recommends consulting a professional for all electrical and plumbing work. 

Vince Barbatano Vince

Vince is Managing Director of Hills Irrigation and is supported by Lisa in an administrative capacity. Andrew, Isaac and Megan look after the day to day needs of both online and shop customers. As Project Manager, Vince is also responsible for installation projects along with his team. It is his responsibility to work closely with clients to ensure that scope of work is understood and followed.