# Nominal Pipe Size NPS, Nominal Bore NB, Outside Diameter OD

What is NPT & what are its applications?

## What is a relation between NPS, NB & OD of a pipe?

Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. Pipe size is specified with two non-dimensional numbers: a nominal pipe size (NPS) for diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness. NPS is often incorrectly called National Pipe Size, due to confusion with national pipe thread (NPT)

NB (nominal bore) is the European designation equivalent to NPS is DN (diamètre nominal/nominal diameter/Durchmesser nach Norm), in which sizes are measured in millimeters. NB (nominal bore) is also frequently used interchangeably with NPS.

OD is the outside diameter of the pipe and is fixed for a given size.

The NPS is very loosely related to the inside diameter in inches, but only for NPS 1/8 to NPS 12. For NPS 14 and larger, the NPS is equal to the outside diameter (OD) in inches. For a given NPS, the OD stays constant and the wall thickness increases with larger SCH. For a given SCH, the OD increases with increasing NPS while the wall thickness increases or stays constant. Pipe sizes are documented by a number of standards, including API 5L, ANSI/ASME B36.10M in the US, BS 1600 and BS EN 10255 in the United Kingdom and Europe, and ISO 65 internationally.

For NPS of 5 and larger, the DN is equal to the NPS multiplied by 25 (not 25.4).

Table below shows the relation between Nominal pipe size, Nominal diameter & outside diameter for pipes:

 Nominal Pipe size NPS [inches] Nominal Diameter DN [mm] Outside Diameter OD [mm] 1/2 15 21.3 3/4 20 26.7 1 25 33.4 1 1/4 32 42.16 1 1/2 40 48.26 2 50 60.3 2 1/2 65 73.03 3 80 88.9 4 100 114.3 5 125 141.3 6 150 168.28 8 200 219.08 10 250 273.05 12 300 323.85 14 350 355.6 16 400 406.4 18 450 457.2 20 500 508 24 600 609.6 28 700 711.2 32 800 812.8 36 900 914.4 40 1000 1016 42 1050 1066.8 44 1100 1117.6 48 1200 1219.2 52 1300 1320.8 56 1400 1422.4 60 1500 1524 64 1600 1625.6 68 1700 1727.2 72 1800 1828.8 76 1900 1930.4 80 2000 2032 88 2200 2235.2 96 2400 2438.4 104 2600 2641.6 112 2800 2844.8 120 3000 3048 128 3200 3251.2

## What is NPT & what are its applications?

NPT is the abbreviation used for National Pipe Thread Taper. It is an American National Standard used to join pipes & fittings. ASME B1.20.1 is the standard used for NPT which covers dimensions and gaging of pipe threads for general purpose.

Most commonly used sizes for pipes & fittings by the U.S. suppliers commonly are 1/8, 1/4, 3/8, 1/2, 3/4, 1, 1 ¼, 1 ½ and 2 inch. Smaller sizes than those listed are occasionally used for compressed air. For sizes larger than 3 inches and above there are other method of joining available so threading is less frequently used in this sizes.

Sometimes NPT threads are referred to as MPT (Male Pipe Thread), MNPT, or NPT (M) for male (external) threads and FPT (Female Pipe Thread), FNPT, or NPT (F) for female (internal) threads.

For details on NPT, refer to clause 3 of ASME B1.20.1SPECIFICATION FOR GENERAL PURPOSE TAPER PIPE THREADS, NPT

Fig 3 American national standard taper thread notation

Click to enlarge the table

Basic dimensions american national standard taper thread- Table 1

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Basic dimensions american national standard taper thread – Table 2