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It is common to identify pipes by inches using NPS or “Nominal Pipe Size

NPT on the other hand stands for National Pipe Thread.

The metric equivalent is called DN or “diametre nominel“.

The metric designations conform to International Standards Organization (ISO) usage and apply to all plumbing, natural gas, heating oil, and miscellaneous piping used in buildings.

The use of NPS does not conform to American Standard pipe designations where the term NPS means “National Pipe Thread Straight”. Based on the NPS and schedule of a pipe, the pipe outside diameter (OD) and wall thickness can be obtained from reference tables such as those below, which are based on ASME standards B36.10M and B36.19M.



Diameter Nominal DN (mm)
Nominal Pipe Size NPS (inches)


Outside diameter (OD)  inches (mm)
6

8

10

15

20

25

32

40

50

65

80

100

150

200

250

¼
½
¾
1
2
3
4
6
8
10
 0.405 in (10.29 mm)
 0.540 in (13.72 mm)
 0.675 in (17.15 mm)
 0.840 in (21.34 mm)
 1.050 in (26.67 mm)
 1.315 in (33.40 mm)
 1.660 in (42.16 mm)
 1.900 in (48.26 mm)
 2.375 in (60.33 mm)
 2.875 in (73.02 mm)
 3.500 in (88.90 mm)
 4.500 in (114.30 mm)
 6.625 in (168.27 mm)
 8.625 in (219.08 mm)
 10.75 in (273.05 mm)

























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