NPT Pipe Thread Size Chart (TPI & OD) | HandySkook
NPT Pipe Thread Size Chart
An NPT (National Pipe Tapered) thread chart showing nominal pipe size, threads per inch and actual outside diameter — for plumbing and fittings.
NPT pipe thread sizes
| Nominal (NPT) | Threads/inch (TPI) | Actual OD (in) |
|---|---|---|
| 1/8" | 27 | 0.405 |
| 1/4" | 18 | 0.540 |
| 3/8" | 18 | 0.675 |
| 1/2" | 14 | 0.840 |
| 3/4" | 14 | 1.050 |
| 1" | 11.5 | 1.315 |
| 1-1/4" | 11.5 | 1.660 |
| 1-1/2" | 11.5 | 1.900 |
| 2" | 11.5 | 2.375 |
NPT sizes are nominal — a “1/2 in” pipe thread is actually 0.840 in across the outside. Threads are tapered to seal; use thread sealant or PTFE tape on the male threads.
Frequently asked questions
Why is NPT pipe size different from the actual diameter?
NPT sizes are nominal, based on the old inner diameter of iron pipe. A 1/2 in NPT thread actually measures 0.840 in on the outside.
Do I need tape on NPT threads?
Yes — NPT threads seal on the taper, so apply PTFE (plumber’s) tape or pipe-thread sealant to the male threads to prevent leaks.
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