NPT Fitting Size Chart: Pipe Diameter & Thread Pitch
NPT fitting sizes can be confusing because the nominal pipe size does not match the fitting’s measured outside diameter. For example, a 1/2-inch NPT fitting has an approximate pipe outside diameter of 0.840 inches—not 0.500 inches.
Use this NPT fitting size chart to compare nominal National Pipe Thread sizes, approximate outside diameters and threads per inch. It can help identify NPT pipe fittings, stainless steel fittings, valves, bulkheads, pumps and other threaded fluid-handling components.
NPT Fitting Size Chart
| Nominal NPT Size | Approximate Pipe OD | Approximate OD in Millimetres | Threads per Inch |
|---|---|---|---|
| 1/16" | 0.3125" | 7.94 mm | 27 |
| 1/8" | 0.405" | 10.29 mm | 27 |
| 1/4" | 0.540" | 13.72 mm | 18 |
| 3/8" | 0.675" | 17.15 mm | 18 |
| 1/2" | 0.840" | 21.34 mm | 14 |
| 3/4" | 1.050" | 26.67 mm | 14 |
| 1" | 1.315" | 33.40 mm | 11.5 |
| 1 1/4" | 1.660" | 42.16 mm | 11.5 |
| 1 1/2" | 1.900" | 48.26 mm | 11.5 |
| 2" | 2.375" | 60.33 mm | 11.5 |
| 2 1/2" | 2.875" | 73.03 mm | 8 |
| 3" | 3.500" | 88.90 mm | 8 |
| 3 1/2" | 4.000" | 101.60 mm | 8 |
| 4" | 4.500" | 114.30 mm | 8 |
| 5" | 5.563" | 141.30 mm | 8 |
| 6" | 6.625" | 168.28 mm | 8 |
| 8" | 8.625" | 219.08 mm | 8 |
| 10" | 10.750" | 273.05 mm | 8 |
| 12" | 12.750" | 323.85 mm | 8 |
Measurements are provided as identification references. Actual male-thread measurements can vary slightly depending on the measurement location, thread taper, manufacturing tolerance and thread condition.
What Does NPT Mean?
NPT stands for National Pipe Taper. It is a tapered pipe-thread standard commonly used throughout North America on pipe fittings, valves, pumps, pressure gauges, bulkheads and fluid-handling equipment.
The male and female threads become tighter as they are assembled. NPT connections normally require an appropriate thread sealant, such as PTFE thread tape or pipe-thread sealant, to create a leak-resistant connection.
Why Is the Measured Diameter Larger Than the NPT Size?
NPT sizes are nominal pipe sizes rather than direct measurements of the thread diameter. A fitting labelled 1/2-inch NPT is designed for the 1/2-inch nominal pipe system, but its approximate outside diameter is 0.840 inches.
This difference is normal. Do not identify an NPT fitting by comparing the nominal size to a ruler measurement alone.
How to Measure a Male NPT Fitting
- Use a caliper to measure across the widest part of the male threads.
- Compare the measurement with the approximate outside diameter in the NPT sizing chart.
- Use a thread-pitch gauge to count or confirm the threads per inch.
- Confirm that the thread is tapered rather than straight.
- Compare the fitting with a known NPT component whenever possible.
How to Identify a Female NPT Fitting
Female NPT threads are more difficult to identify using only an inside-diameter measurement. Measure the thread opening with a caliper, check the thread pitch and compare the fitting with a known male NPT component or thread-identification gauge.
Do not force a male fitting into an unknown female connection. Similar-looking NPT, NPS, BSPT and BSPP threads may begin to engage without being properly compatible.
NPT Versus BSP Threads
NPT and BSP pipe fittings are different thread standards. They use different thread forms and may have different pitches, even when their nominal sizes appear identical. NPT and BSP fittings should not be assumed to be interchangeable.
Always identify the thread standard as well as the nominal fitting size before purchasing an adapter, valve or replacement component.
Shop NPT Pipe Fittings
Browse stainless steel NPT pipe fittings, adapters, elbows, tees, reducers, nipples, couplings, caps, plugs and related fluid-handling hardware available from Canuck Homebrew Supply.
If you are unsure which NPT fitting size you require, compare the fitting’s outside diameter and thread pitch with the chart above. Photographs, measurements and information about the connecting equipment can also help with fitting identification.