NPT (American National Standard Taper Pipe Threads) Size Chart

The Definitive NPT Size Chart: Precision Dimensions for Tapered Pipe Systems

Engineering Standard
All NPT dimensions and specifications provided are engineered according to the ASME B1.20.1 standard. These threads feature a mandatory 1:16 taper rate, creating a mechanical interference fit designed for pressure-tight sealing in North American piping systems.

NPT Thread Size Chart with TPI and Taper Dimensions for Pipe Fittings

Understanding NPT (National Pipe Taper) Threads

NPT (National Pipe Taper) is the U.S. standard for tapered threads used on threaded pipes and fittings. Governed by the ASME B1.20.1 standard, NPT threads are uniquely designed to create a leak-proof pressure seal through a principle known as "thread interference."

Unlike parallel threads (such as BSPP or Metric), NPT threads feature a specific 1:16 taper rate (3/4" per foot) along the axis. As the male and female fittings are threaded together, the flanks of the threads compress against each other, creating a tight mechanical seal. Due to the inherent design, tiny gaps may remain at the crests and roots; therefore, the use of thread sealant (PTFE tape or pipe dope) is mandatory to ensure a 100% airtight and watertight connection in hydraulic and pneumatic systems.

Quick Navigation: What You Will Learn

NPT Thread Size Chart: Detailed dimensions including TPI, pitch, and diameters.
Taper Explained: Why the 1:16 taper rate is critical for pressure-tight sealing.
NPT vs. NPS: Key differences between Tapered and Straight pipe threads.
Installation Tips: Best practices for using PTFE tape and thread sealants.
Downloadable Guide: Get the 1-page Thread Comparison PDF for your workshop.

1. What are the Characteristics of National Pipe Taper NPT threads

NPT that are also known as ANSI/ASME B1.20.1 Pipe Threads have some basic characteristics as follows:

There is an angle of 1° 47' 24" (1,7899°) between the taper and the center axis.
They contain a flat truncation of roots and crests.
They possess a thread angle of 60°.
Their pitch is measured in TPI (Threads per Inch).

NPTs are widely used in hydraulic circuits as leak-proof sealants. The pipe threads that are used in applications like hydraulic circuits can be mainly classified into two types as follows:

Jointing threads: Jointing threads are NPTs that are used for joints where there is a requirement of pressure tight area by sealing on the threads and are taper external and parallel or taper internal. In this type of pipe threads, the sealing effect can be improved by using a jointing compound.
Fastening threads: Fastening threads are pipe threads on which pressure tight joints are not made on the threads. In fastening threads, both threads are parallel and the sealing is affected by compression of a soft material or a flat gasket on the external thread.

2. What is the Size Chart of NPT- American National Standard Taper Pipe Threads

Pipe thread sizes are based on the inside diameter (ID) or flow size. If you find an LH added to the mentioned size the. The pipe has a left hand thread.

For instance, "½-14 NPT" marked on a pipe thread means that there is a diameter of ½ inch and 14 threads to each inch and that is made according to the NPT standard.

Nominal Size (inch)	TPI (Threads Per Inch)	Pitch (inch)	Major Dia. (inch)	Tap Drill (inch)
1/16" - 27	27	0.0370	0.3125	1/4" (0.250)
1/8" - 27	27	0.0370	0.405	R (0.339)
1/4" - 18 ★	18	0.0555	0.540	7/16" (0.437)
3/8" - 18	18	0.0555	0.675	37/64" (0.578)
1/2" - 14 ★	14	0.0714	0.840	23/32" (0.718)
3/4" - 14	14	0.0714	1.050	59/64" (0.922)
1" - 11.5 ★	11.5	0.0869	1.315	1-5/32" (1.156)
1-1/4" - 11.5	11.5	0.0869	1.660	1-1/2" (1.500)
1-1/2" - 11.5	11.5	0.0869	1.900	1-47/64" (1.734)
2" - 11.5	11.5	0.0869	2.375	2-7/32" (2.218)
2-1/2" - 8	8	0.1250	2.875	2-5/8" (2.625)
3" - 8	8	0.1250	3.500	3-1/4" (3.250)
4" - 8	8	0.1250	4.500	4-1/4" (4.250)

* Note: NPT threads require thread sealant (PTFE tape or pipe dope) to ensure a pressure-tight seal. ★ indicates most common industrial sizes.

Pro Tip for Engineers: After finding your required dimensions in the NPT chart above, use calipers to verify the thread gender. Remember that male NPT threads are measured on the outside, while female threads are measured internally. If you’re unsure which one you have, our Male vs Female Fitting resource provides the specific measurement points for both.

4. What is Applications of NPT (National Standard Taper Pipe Threads)

NPT pipes are used in a wide variety of applications ranging from electrical conduits to high-pressure piping that carry natural gas and chemically reactive and aggressive liquids.

Some applications that use NPT are as follows:

Pneumatic systems
Hydraulic systems
Plumbing and fittings
Fire protection systems
Chemical industry
Processing industry
Agricultural industry
Irrigation systems
Control systems
Air-conditioning systems

NPT threaded plastic fittings can be readily found as they are standard. However, there are distinct and specific installation and sealing recommendations for installations involving plastic Vs metals. Also, both thread types have installation methods that are different based on gauging the threads for conformance before true installation is complete.

Although these standards are manufactured in order to maintain the uniformity in fittings, tapered pipe threads can become unreliable over time. Due to the continued usage and repair, the threads can become damaged and susceptible to leakage. As a result of this, the area on the pipe where the crest and the root of the thread meet can form a spiral leak path. When this happens, no amount of tightening can make the joint leak proof.

To face this situation, a leak proofing sealant is used. Most of the time, Teflon based sealant is recommended and used on all plastic pipe threads. Most commonly, Teflon tape is wrapped in about two to three turns around the male thread before the final assembly.

Sometimes, liquid Teflon based sealants are also used in order to ensure a pressure tight seal. However, it is always important to ensure that sealants are applied with maximum care so as to prevent from introducing the sealant materials into the flow path of the system.

5. Conclusion

NPT or National Pipe Taper Thread Standard is the most commonly used standard for pipe threads throughout the United States and Canada.

NPT provides a reliable seal for pipes that are used for transportation of hydraulic fluid as well as other liquids, gases and steam. NPTs can be seen to be used in materials like PTFE, PVC, nylon bronze and cast iron, in addition to steel and brass. Among many other thread standards, NPT remains one of the most commonly used standards due to their versatile applications.

What is the taper angle of an NPT thread?

NPT threads have a 60-degree thread angle and a taper rate of 1/16 inch per inch (3/4 inch per foot) along the axis. This taper allows the threads to form a seal when torqued as the flanks of the threads compress against each other.

Is NPT compatible with BSPP or BSPT?

No. NPT (60° angle) is not compatible with BSPP or BSPT (55° angle) due to different thread forms and pitches. Forcing them together will cause leaks and permanent thread damage.

Does NPT thread require sealant?

Yes. Because NPT relies on thread interference, a thread sealant like PTFE tape or a pipe dope is required to fill any remaining gaps between the crests and roots to ensure a 100% leak-proof connection.