NPT Thread Chart (Printable)
Threads per inch and actual thread diameter for NPT sizes 1/16″ through 2″ per ASME B1.20.1. Covers the taper and the diameter only — engagement lengths and gauge dimensions belong in the standard itself.
NPT sizes, TPI and thread diameter
| NPT size | Threads per inch | Basic major dia at thread end (in) | Dia (mm) |
|---|---|---|---|
| 1/16 | 27 | 0.3125 | 7.94 |
| 1/8 | 27 | 0.405 | 10.29 |
| 1/4 | 18 | 0.540 | 13.72 |
| 3/8 | 18 | 0.675 | 17.15 |
| 1/2 | 14 | 0.840 | 21.34 |
| 3/4 | 14 | 1.050 | 26.67 |
| 1 | 11.5 | 1.315 | 33.40 |
| 1-1/4 | 11.5 | 1.660 | 42.16 |
| 1-1/2 | 11.5 | 1.900 | 48.26 |
| 2 | 11.5 | 2.375 | 60.33 |
How to use this chart
NPT is a tapered thread — 1 in 16 on diameter, a 3/4-inch diameter change per foot of length — and it seals on the thread flanks with sealant, not on a gasket. The nominal size is not the diameter: a 1/2 NPT thread measures 0.840 inch at the basic major diameter, matching its pipe's OD in sizes 1/8″ and up. Listed diameters are the basic values at the thread-end reference; manufactured threads carry tolerance and inspection happens at the gauge plane defined in ASME B1.20.1.
NPTF (dryseal) shares the taper and TPI pattern but controls crest and root truncation so the joint can seal metal-to-metal with less reliance on sealant — an NPTF part is not a substitute for NPT by default. From our guide: NPT vs G (BSP) threads. State thread standard and size per line on theRFQ.