Skip to content
Home >> Plumbing >> IPS Vs NPT: A Comprehensive Comparison

IPS Vs NPT: A Comprehensive Comparison

Even though IPS and NPT connections are often considered interchangeably, in truth they are not the same. Yes, there are some similarities between the two. However, just from the name, you can tell the difference.

The most confusing one is solving the debate for IPS vs NPT. What’s the difference? The IPS sizing system comes with a straight thread, and NPT has a tapered thread. So, their functionality is a little different in specific workspaces, even though they look similar.


In this post, we are here to break down everything so that you can eliminate the confusion once and for all.

What Is An IPS Pipe Connection?

The IPS connection (Iron Pipe Size) dates back to the nineteenth century. So, yes, it’s an older system. Iron pipe size or IPS categorizes the thickness of the pipe walls.

Initially, IPS pipe was used for sizing wrought iron pipes. Even though the connection standard is backdated, it’s still found in iron, steel, brass, and PVC plumbing parts.

Yes, understanding the critical difference can be a bit confusing for DIYers. It’s because of the naming structure. You can often find FIPS or MIPS threading on plumbing fittings. This threading is derived from the IPS system.

A lot of people think the IPS connection is only for threaded fittings. So, it’s best suited for iron pipes (as they are threaded). But that’s not the case. There are many PVCs that use this type of connection. The question is, why?

As you can see, the IPS standard is concerned with the outer dimension of the pipe. It’s more suited for durable household connections, mainly underground piping systems. The external size of a standard PVC is similar to that of a steel pipe.

Where To Use The Ips Pipe Connection?

You can use an IPS pipe connection with NPT pipes. Well, the standard for threading IPS pipe is NPT. IPS or NPT – no matter its label, both parts will fit together. So, where to use IPS fittings?

To understand that, we need to look at its prominent performance characteristics. As it turns out, the thermal conductivity and power consumption rate for IPS pipes are low. That’s why they are best for hydronic heating systems.

Using an IPS pipe thread in a hot water system quickly helps in reducing heat loss. What’s more, IPS pipes offer extended service life. It is vital for such connections.

What Is An NPT Pipe Connection?

National Pipe Tapered Thread is the full form of NPT. It’s also known as ANSI/ASME B1.20.1 pipe threads. Like most other metrics, this is a unique measurement for pipe threads for the USA.

This type of connection has been widely used in the US for over 100 years. It means NPT pipes are readily available. Not just that, NPT pipes come in different shapes and sizes.

By now, you can tell NPT is a widely used and pretty well-known system. It’s because the NPT connection offers an easy assembly. And the connection system is so easy that you can connect them without flaring tubes, seals, or o-rings.

However, NPT pipes are initially designed for waterline plumbing tasks. But they are not suited for hydraulic systems. Nevertheless, a lot of plumbers still use them for hydraulic systems. Anyway, there’s always the additional risk of leakage on the water pipe.

Where To Use The Npt Pipe Connection?

You can use NPT connections to seal pipes for fluids and gas transfer. Now, it’s true that NPT connections cannot handle fluid pressures from hydraulic systems. But you can still use them. All you need to do is, make a good choice.

Finding NPT pipes is not complex as they are readily available. For low-pressure connections, you need iron or brass NPT connections. And for high-pressure connections, choose carbon or stainless steel pipes.

The most significant flaw of NPT pipes is the leakage issue under high pressure. Why is that? It’s because these types of pipes rely on thread deformation. It means the connection has a metal-to-metal sealing design. For this reason, NPT pipes are best for one-time assembly.

What does that mean? NPT connections are best for places where you won’t assemble and disassemble the connection too often. Why? If you disassemble and assemble NPT connections too often, the threads will deform quickly. As a result, there will be leakage. That’s not a good sight.

IPS Vs NPT: Comparison Chart

Let’s have a look at the key differences between the two sizing systems at a glance:

Thread TypeStraightTapered
MeasurementBased on the pipe wall thickness and the inside diameter of the pipeBased on a thread per inch, and the outside diameter
UsageHydraulic water system agricultural sector indoor/outdoor faucetPower plants gas station oil stations manufacturing industry natural gas lines chemical supply compressed air
SealingNo need to use PTFE tapeYou need PTFE tape for sealing
AdvantagesPVC pipe and fittings utilize IPS standards to create a watertight seal. This fitting increases the longevity of the system nominal Pipe Size (NPS) is used interchangeably with IPS sizing    Readily available widely known and used offers simple assembly

What Are The Differences Between Ips And Npt Pipe Connection?

It’s easy to get confused for DIYers to understand the primary difference between IPS and NPT connections. But when you know the difference, you can quickly choose which one to pick. Here we are discussing them in detail:


The angle between the taper and center axis for both the connection remains the same (1° 47′ 24″). In terms of characteristics, both of the pipes are similar. That’s why understanding the difference becomes confusing. Even you measure the pitch in threads per inch or TPI. So, there’s not much difference in characteristics between the two.

In terms of characteristics, they may not differ that much. But the measurement dimension is different for both pipes. You measure IPS pipes through wall thickness and inner dimension. But for NPT pipes, you count thread per inch and outer dimension.


IPS connections are readily available in multiple sizes, including 1-inches, ½-inches, and ¼-inches. For IPS connections, you need to measure the inner diameter of the pipe. It’s because IPS thread dimensions have a simple threading structure. The internal threading connects all the fittings in place.

But that’s not the case for NPT pipes. In order to measure NPT pipes, you need to consider the inner and outer diameters. The typical sizes for these pipes are 1/8, ¼, 3/8, ½, ¾, 1, 1 ¼, 1 ½, and 2 inches. These are most common for us fittings and connections.

However, sizes lower than ⅛-inches are sometimes used for compressed-air supplies. Sizes lower than that are rare, mainly because you can employ the joining method with larger pipes.

To help you understand better, we are sharing the sizing chart for both sizing systems:

Sizing for IPS (Iron Pipe Straight)

Thread/SizeODM (Outside Diameter for Male)TPI (Thermoplastic Isolator)
1 ½-inches1.87811.5

Sizing for NPT (National Pipe Tapered)

Thread/SizeODM (Outside Diameter for Male)TPI (Thermoplastic Isolator)
1 ½-inches1.90011.5

If you closely look at the sizing table, you will notice the TPI for both systems is the same. However, the ODM is slightly different. Even though the difference is insignificant in numbers, this is the main reason NPT and IPS don’t work together.

Pipe Connectors

Among the critical difference between the two types of connection, a key factor to consider is the types of pipe connectors. Primarily, it gets incredibly confusing for PVC pipe thread.

To understand the difference, you must learn the male and female specifications. So, what are they?

Male connectors look like bolts as they have threading on the outside. On the other hand, female connectors resemble a nut because they have threading on the inside.

It’s essential to select the connector type for any pipe. Now, if both IPS and NPT pipes have male and female threading, how do they separate from each other? That’s easy. Have a look at the threading type. IPS pipes have a straight thread. So, it helps you seal onto the fitting like a washer.

On the other hand, NPT comes with tapered thread. It’s designed to seal on the threads. For this reason, you need to put pipe tape to lubricate the pipes. Mainly, the tape will deform the thread and create a seal.

That’s why NPT connections are one-time connections. On the other hand, you can remove or install IPS connections as many times as you please.

Leakage Issues

There are no visible leakage issues in IPS connections. An IPS pipe is cut in halves and welded together. And it’s the internal dimension that matter the most. Also, the straight threading design ensures there’s no leakage.

But NPT connections tend to leak. Before you assemble NPT fittings, you need to attach a sealant. Overtightening (for female port) or under-tightening (male port) can cause problems. You have to stay careful during assembly.

You don’t have to worry about such problems with IPS connections.

Ips Or Npt Which One To Choose?

Still a little bit confused, right? Well, we can understand. When making a buying choice, you must realize that what you buy should be perfect for the job. Well, there’s no doubt the IPS system is ideal for both business and household usage.

But NPT is widely available. That brings us to confusion, is shower arm NPT or IPS? Most shower arms in the US use the NPT system. It’s because NPT is the modern version, and IPS is a bit old school.

However, it still has appeal to a lot of plumbing systems. Significantly, the IPS system is best for hydraulic water connections. It’s an excellent match for scheduled 40 or 80 iron plumbing pipes. You see, 80 pipes are widely used in the agricultural and industrial sectors. Even IPS systems ensure a stable connection for household faucets and hot water supplies.

That doesn’t mean NPT is there just because it’s a modern tech and widely available. Tapered threads create a reliable seal to carry fluid, gas, or steam through the pipeline. That’s why oil, gas, chemical, manufacturing, and power plants use NPT.

Both offer good support for household water connections. But the obvious choice is when you try to implement them in a specific industry or business space.


That’s about all for IPS or NPT systems. Now, you can tell the basic difference between the two. Yes, at first, they seem to look the same. But some differences set them apart from each other.

This brings us to a conclusion, another question to be exact. Between IPS vs NPT, which one would you pick? That’s easy. First, you analyze the central piping system or corresponding system. Once you recognize the primary system connection, choosing a suitable pipe won’t be hard anymore.

Further Read:

Can PVC Pipe Be Buried In Concrete?

How to chlorinate a water system?