NPT Pipe Size Identification
To identify the size of an NPT (National Pipe Thread) fitting, you'll need to measure either the outside diameter (OD) of the male NPT thread or the inner diameter (ID) of the female NPT thread. The NPT thread size is not the same as the nominal pipe size, so a direct measurement of the pipe itself won't give you the correct NPT size. Instead, you'll need to compare your measurements to a standard NPT sizing chart, like the one shown below.
Here's How to Measure:
- Identify the NPT Thread Type: Determine if the thread is male (external) or female (internal)
- Measure the Thread:
• Male Threads: Use a caliper or other measuring tool to measure the outside diameter (OD) of the male thread, preferably at the base of the threads.
• Female Threads: Measure the inside diameter (ID) of the female thread. - Consult a Standard NPT Sizing Chart (Sample Below): Compare your measurement to a standard NPT sizing chart, which will list the corresponding nominal pipe thread size for each OD or ID measurement.
Important Notes to Consider when determining the NPT Thread Size you need:
- NPT threads are tapered: This means the outside diameter of a male thread is larger at the base of the thread and tapers towards the end.
- NPT sizes are based on the inside diameter of the pipe: The nominal size of an NPT thread doesn't directly correspond to the outside diameter of the pipe.
- Use a pipe thread gauge for accuracy: While a caliper can be used for identification, a pipe thread gauge is the most accurate method.
- We recommend thatn you always use PTFE tape or suitable pipe joint compound: NPT threads are designed to seal when tightened, but it's always a good idea to use a sealant to prevent leaks.
The below condensed chart may help you determine the NPT pipe thread size you need. This chart applies to NPT pipe threads used in the USA. This chart may not be accurate for determining pipe threads from Europe, Asia, and other parts of the world.
