IPS VS NPT – All You Need to Know Before Buying

What is the difference between IPS and NPT piping? IPS stands for Iron Pipe Straight, and NPT stands for National Pipe Tapered. So, the name itself depicts the difference. IPS refers to a pipe sizing system with a straight thread, whereas NPT is a standard in plumbing for the tapered thread. 

These are two of the pipe thread standards that people most often get confused about. Here we will discuss all the significant differences between IPS vs NPT

IIPS VS NPT – Differences at a Glance

NPT (National Pipe Tapered)IPS (Iron Pipe Straight)
Thread Type
A standard for pipe with tapered thread A standard for pipe with straight thread
Based on Inside Diameter (ID) and pipe wall thickness Based on Outside Diameter (OD) and Threads Per Inch (TPI)
Requires PTFE tape for a leak-proof sealDoes not require PTFE tape
Natural gas line, Shower armIndoor/outdoor faucet

These are some basic differences. Now, let’s get to know more about IPS vs NPT pipe. The comparison will be based on the following points:

  • Thread Type
  • Origin
  • Measurement
  • Sizing
  • Usage

Thread Type

There’s a common question always buzzing around when it comes to plumbing: What is IPS thread? Though some sources on the internet refer to IPS as Iron Pipe Size, it actually means Iron Pipe Straight thread. This means it’s a standard sizing for straight or parallel pipe threads. 

On the other hand, the NPT, known as the National Pipe Tapered, is ideal for tapered thread pipes. Now, if you are a newbie, you might be wondering what a tapered pipe is.

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If a pipe thread becomes narrow as it goes inward, i.e., the diameter decreases in the threaded section as it goes down, it is called a tapered thread. In general, a 1° 47′ 24″ (1.7800°) angle is formed between the taper and the pipe’s center axis.

Now, you might be clear enough with the basic difference between IPS vs NPT threads.


The IPS system emerged during the early 19th century and was a popular measurement technique until WW2 ended. This system was highly practiced in the US and the UK. However, many pipe manufacturers around the world still use IPS measurements. 

In 1864, William Sellers established the National Pipe Tapered (NPT) thread as the standard for nuts, bolts, and screws in the United States. The American Industrial Revolution was made possible by his 60-degree thread angle, which early American clockmakers widely used. Later on, these thread measurements were adopted as the American National Standard.


The methods of measuring both the pipes are quite different from each other. For the IPS fitting system, the inside diameter (ID) and the thickness of the pipe wall are measured.

Also Read: MIP Vs NPT – The Better Type For Your Needs?

In the case of NPT pipes, the pipe’s outside diameter (OD) or the fitting measurement comes with the threads per inch (TPI). There’s a possibility of having the same TPI for different pipe sizes; that is why both the TPI and the OD are necessary for proper thread size identification.


The commonly used sizes for IPS threads include ⅛, ⅜, ¾, ¼, ½, 1, 1 ½,  and 2 inches. 

⅛, ¼, ⅜, ½, ¾, 1, 1 ¼, 1 ½, and 2 inches are the common sizes for NPT pipes. Most American suppliers adopt them on their pipes and fittings.

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Another frequently asked question is: Are NPT and IPS the same thread size? The simple answer is “No.”

The examples in the following chart will distinguish the sizes between these two pipes:


Many manufacturers of polyvinyl chloride, iron, piping, and PVC that link the faucets use the IPS system for their piping and fittings. As a result, they are appropriate for both business and household use.

IPS pipes mainly work well together with the schedule 80 or 40 plumbing iron pipes. Because of being stronger, the schedule 80 pipes have vast use in the agriculture sector. The IPS faucets are also a good fit for both indoor and outdoor use.

Now there’s another confusion: Is shower arm NPT or IPS? Well, most shower arms are NPT. In the United States, a 1/2-inch NPT is the common thread size for modern showerheads.

Moreover, a tapered threaded pipe is also a reliable seal for pipelines carrying liquids, gases, steam, or hydraulic fluid. As a result, oil and gas, chemical, power plants, and manufacturing industries use the NPT fitting.

Frequently Asked Questions (FAQs)

Can I use NPT with IPS?

The dimensions of NPT and IPS are slightly different. Thus, NPT and IPS cannot be used together.

Are shower arms IPS or NPT?

The NPT, i.e., the pipe with a tapered thread, is generally used for the shower arm connectors. In the United States, 1/2-inch NPT is the common thread size for modern showerheads.

What is an IPS supply line?

IPS or Iron Pipe Straight is an older standard of the piping system that measures the thickness of the pipe wall. Some iron or PVC pipe manufacturers still follow this measurement. An IPS supply line can connect to faucets for both indoor and outdoor usage.


So, you have learned how the IPS differs from the NPT. Still, a question might appear in your mind: Can I use an NPT to IPS adapter

In the comparison table from the sizing section, you can see that the TPI of both the pipes is the same, but the OD slightly varies. That is the reason why the NPT and the IPS won’t work together. 

Now, which one would you use between IPS Vs NPT? The answer is simple. Before deciding on any of these two systems, you have to check the main system or the corresponding piping system where you intend to work. If you can recognize whether it is an NPT or IPS, then you may proceed accordingly.

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