NPT Size Chart – National Standard Taper Pipe Thread [PDF]

What is NPT Size Chart?

The National Pipe Thread (NPT) is a common type of threading used in plumbing and piping systems. It is a tapered thread that creates a seal between two pipes, preventing leaks and ensuring the proper flow of fluids. NPT threads are standardized and come in a variety of sizes, which can be confusing for those who are not familiar with the system. That is where an NPT size chart comes in handy. An NPT size chart provides a comprehensive guide to the various sizes of NPT threads, including their corresponding dimensions and measurements.

What is NPT Thread size chart?

Common NPT Thread Sizes

The most commonly used sizes for NPT threads are 1/8″, 1/4″, 3/8″, 1/2″, 3/4″, 1″, 1-1/4″, 1-1/2″, and 2″. These sizes refer to the diameter of the pipe that the thread will be used on. It is important to note that NPT threads are tapered, meaning they get narrower towards the end. This taper allows for a tight seal when the threads are tightened together. Understanding the common sizes of NPT threads is essential for anyone working with pipes and fittings, as it ensures proper fitting and sealing of connections.

NPT Threads Diagram

ASME/ANSI Standards

NPT, or National Pipe Thread is defined by the ASME/ANSI standard B1.20.1, which sets the specifications for the thread’s dimensions, tolerances, and thread form. The ASME/ANSI standard B1.20.1 also specifies the manufacturing process for NPT threads, including the use of special cutting tools and inspection procedures. Adhering to this standard ensures that NPT threads are consistent and reliable, which is essential for the safety and performance of any plumbing or piping system.

Read More : Pipe Joints

What is Nominal Pipe Size (NPS)?

Nominal Pipe Size (NPS) is a standardized system of dimensions for pipes used in various industries. It refers to the inner diameter of the pipe and is expressed in inches. The NPS system is used to ensure consistency in the manufacturing, installation, and maintenance of pipes across different regions. The NPS system is widely used in the United States. NPS is an important factor to consider when selecting pipes for a particular application, as it determines the flow rate and pressure capacity of the pipe. The NPS system includes different schedules, which indicate the thickness of the pipe wall. The higher the schedule number, the thicker the pipe wall.

NPT Size Chart

Diameter (D)
Nominal Pipe SizeThreads Per Inch (Pitch)Threads Pitch Length (P)Pitch Diameter at External Thread Start (E0)Hand Tight Thread Engagement Length (L1)Diameter (E1)Maximum Thread Engagement (L2)Diameter (E2)

Difference between NPT Threads & BSPT Threads

Credits : Jianzhi Pipe Fitting

How to measure Pipe Threads?

Credits : Air Compressor Parts Online


Are Nominal Pipe Size (NPS) & National Standard Taper Pipe Thread (NPT) the same standards ?

It is important to note that NPS and NPT are different standards with different measurements. NPT threads have a slightly larger diameter than NPS pipes, which allows them to create a tight seal. Understanding the relationship between NPS and NPT is crucial for anyone working in the plumbing or piping industries. For example, a 1-inch pipe will have a 1-inch NPT thread.

How to use the NPT Thread Chart?

To use the NPT thread chart, start by determining the size of the pipe. This can usually be found stamped on the side of the component, or by measuring the outer or inner diameter of the pipe. Once you have the size, consult the chart to determine the correct thread type. This will be designated by a letter code next to the size.

Next, use the chart to determine the number of threads per inch for the chosen thread type. This will be listed in a separate column next to the size and thread type. It is important to match the number of threads per inch with the corresponding fitting or pipe. Mismatched threads can result in leaks or other problems.

Finally, use the chart to determine the appropriate torque values for tightening the fitting or pipe. This will help ensure that the connection is secure and leak-free.


In conclusion, understanding the NPT thread size chart is crucial for anyone working with pipes and fittings. Choosing the right thread size is important to ensure a leak-proof and secure connection. The chart provides a clear and concise guide for selecting the appropriate thread size based on the pipe diameter and thread pitch.

Print Friendly, PDF & Email