Pipes are extensively used in mechanical engineering, from the Oil & Gas industry and their offshore rigs to the more simplistic home tap water networks, these hollow sections made of metal or plastics are essential for a very wide spectrum of applications. Before we head into the details of their standardization, it is important to identify their primary geometrical features and what dimensions we measure and define for all pipes. First and foremost, since pipes are hollow tubes, they have an outer diameter and an inner diameter dimension. This has caused confusion in the past since some industry sectors or pipe manufacturers chose to identify the outer or the inner diameter as the nominal pipe size, and so problems of consistency arose.

## Pipes And Their Dimensions

In order to keep consistency with the pipe fitting sections, we have nowadays decided to relate the outer diameter with the **“nominal pipe size”** classification, so when we’re dealing with an one-inch pipe we can consult data tables and figure out its specific **“outer diameter”**. Next, there is the **“wall thickness”** of the pipe that is used by engineers to determine whether a pipe section is suitable to handle the designated pressures or not, categorized in **“schedules”**. The pipe’s wall thickness practically determines the strength of the pipe but it also helps us derive the **“inner diameter”** of the pipe. Based on the aforementioned consideration, we can simply calculate the inner diameter of a pipe by subtracting the pipe wall thickness twice from the number that corresponds to the outer diameter. This consideration is important for engineers since the inner diameter is what determines the flow velocity and rate. For example, a pipe that has an outer diameter of 60.3 mm and a wall thickness of 2.8, has an internal diameter of 60.3 – (2.8 x 2) = 54.7 mm.

## Different Dimensioning Standards

Considering how widely these elements are applied in practical engineering, it is very important to be able to ensure coherence between them (fitting and connecting/welding sections) as well as to predict their performance from the perspective of fluid flow, and thus pipe sizes are fully standardized. Usually, engineers use a term called **“nominal bore”** which corresponds to a certain outer diameter measured in inches, or the **“nominal diameter”** which corresponds to an outer diameter measured in millimeters. These sizes are based on an approximation and are not characteristic of the exact diameter of the pipe. For example, the actual diameter of a pipe that has a nominal bore of two inches isn’t exactly two inches or 50.8 millimeters, but 2.37″ or 60.3 mm. This means that there is always a standard corresponding value for each nominal bore category, indicating the pipe’s outer diameter. Engineers can find that value in data tables and never try to follow a “data reduction” approach as this won’t work in this case.

As per the ANSI/ASME, ISO, ACPA, EN, BS, and DIN standards, all pipes are classified as per their “nominal bore” or “nominal diameter” and their “schedule”. Based on that, the internal diameter is given through tables. There are also other standards such as the IPS, the JIS, the DIPS, and the PIP, but those are limited, obsolete, and/or too specialized. Obviously, there are many pipe sizes to address every possible need, but I will provide a data table covering the sizes that are most commonly used in the industry starting from a half-inch diameter and up to eight inches. The schedule rating categories that indicate the wall thickness range from 5 to 160, indicating an increasing thickness value. It is also important to note that for practical reasons, the edge of pipes are often colored according to their schedule rating and this is also standardized. Green corresponds to extra light thickness, yellow corresponds to light thickness, blue to medium, red to heavy, and white to extra heavy wall thickness. To relate these with the schedule ratings, the medium is schedule – 40, and the heavy is schedule – 80. Of course, the higher the thickness the higher the weight, and this very important consideration can also be attained by data tables provided by the pipe manufacturer.

## Pipe Size Chart (1/8″ – 24″ Nominal Bores)

Nominal Bore | Nominal Diameter | Outer Diameter | Schedule 40 Wall Thickness | Schedule 40 Weight | Schedule 40 Internal Diameter | Schedule 80 Wall Thickness | Schedule 80 Weight | Schedule 80 Internal Diameter |

1/8″ | 6 mm | 0.405″ / 10.29 mm | 0.068″ / 1.73 mm | 0.37 kg/m | 0.269″ / 6.84 mm | 0.095″ / 2.41 mm | 0.47 kg/m | 0.215″ / 5.84 mm |

1/4″ | 8 mm | 0.540″ / 13.72 mm | 0.088″ / 2.24 mm | 0.63 kg/m | 0.364″ / 9.22 mm | 0.119″ / 3.02 mm | 0.8 kg/m | 0.302″ / 7.66 mm |

3/8″ | 10 mm | 0.675″ / 17.15 mm | 0.091″ / 2.31 mm | 0.84 kg/m | 0.493″ / 12.48 mm | 0.126″ / 3.2 mm | 1.1 kg/m | 0.423″ / 10.7 mm |

1/2″ | 15 mm | 0.840″ / 21.34 mm | 0.109″ / 2.77 mm | 1.27 kg/m | 0.622″ / 15.76 mm | 0.147″ / 3.73 mm | 1.62 kg/m | 0.546″ / 13.84 mm |

3/4″ | 20 mm | 1.05″ / 26.67 mm | 0.113″ / 2.87 mm | 1.69 kg/m | 0.824″ / 20.96 mm | 0.154″ / 3.91 mm | 2.2 kg/m | 0.742″ / 18.88 mm |

1″ | 25 mm | 1.315″ / 33.4 mm | 0.133″ / 3.38 mm | 2.5 kg/m | 1.049″ / 26.64″ | 0.179″ / 4.55 mm | 3.24 kg/m | 0.957″ / 24.3 mm |

1-1/4″ | 32 mm | 1.66″ / 42.16 mm | 0.14″ / 3.56 mm | 3.39 kg/m | 1.38″ / 35.08 mm | 0.191″ / 4.85 mm | 4.47 kg/m | 1.278″ / 32.5 mm |

1-1/2″ | 40 mm | 1.9″ / 48.26 mm | 0.145″ / 3.68 mm | 4.05 kg/m | 1.61″ / 40.94 mm | 0.2″ / 5.08 mm | 5.41 kg/m | 1.5″ / 38.14 mm |

2″ | 50 mm | 2.375″ / 60.33 mm | 0.154 ” / 3.91 mm | 5.44 kg/m | 2.067″ / 52.48 mm | 0.218″ / 5.54 mm | 7.48 kg/m | 1.939″ / 49.22 mm |

2-1/2″ | 65 mm | 2.875″ / 73.02 mm | 0.203″ / 5.16 mm | 8.63 kg/m | 2.469″ / 62.68 mm | 0.276″ / 7.01 mm | 11.41 kg/m | 2.323″ / 58.98 mm |

3″ | 80 mm | 3.5″ / 88.9 mm | 0.216″ / 5.49 mm | 11.29 kg/m | 3.068″ / 77.92 mm | 0.3″ / 7.62 mm | 15.27 kg/m | 2.9″ / 73.66 mm |

3-1/2″ | 90 mm | 4″ / 101.6 mm | 0.226″ / 5.74 mm | 13.57 kg/m | 3.548″ / 90.12 mm | 0.318″ / 8.08 mm | 18.64 kg/m | 3.364″ / 85.44 mm |

4″ | 100 mm | 4.5″ / 114.3 mm | 0.237″ / 6.02 mm | 16.08 kg/m | 4.026″ / 102.26 mm | 0.337″ / 8.56 mm | 22.32 kg/m | 3.826″ / 97.18 mm |

5″ | 125 mm | 5.563″ / 141.3 mm | 0.258″ / 6.55 mm | 21.77 kg/m | 5.047″ / 128.2 mm | 0.375″ / 9.53 mm | 30.97 kg/m | 4.813″ / 122.24 mm |

6″ | 150 mm | 6.625″ / 168.27 mm | 0.28″ / 7.11 mm | 28.26 kg/m | 6.065″ / 154.08 mm | 0.432″ / 10.97 mm | 42.56 kg/m | 5.761″ / 146.36 mm |

8″ | 200 mm | 8.625″ / 219.08 | 0.322″ / 8.18 mm | 42.55 kg/m | 7.981″ / 202.74 mm | 0.5″ / 12.7 mm | 64.64 kg/m | 7.625″ / 193.7 mm |

9″ | 225 mm | 9.625″ / 244.5 mm | 0.342″ / 8.69 mm | 50.54 kg/m | 8.941″ / 227.12 mm | 0.5″ / 12.7 mm | 72.6 kg/m | 8.625″ / 219.1 mm |

10″ | 250 mm | 10.75″ / 273 mm | 0.365″ / 9.27 mm | 60.29 kg/m | 10.02″ / 254.46 mm | 0.594″ / 15.09 mm | 95.98 kg/m | 9.562″ / 242.82 mm |

11″ | 275 mm | 11.75″ / 298.5 mm | 0.375″ / 9.53 mm | 67.91 kg/m | 11″ / 279.44 mm | 0.5″ / 12.7 mm | 89.51 kg/m | 10.75″ / 273.1 mm |

12″ | 300 mm | 12.75″ / 323.8 mm | 0.375″ / 9.53 mm | 73.86 kg/m | 12″ / 304.74 mm | 0.688″ / 17.48 mm | 132.05 kg/m | 11.375″ / 288.84 mm |

14″ | 350 mm | 14″ / 355.6 mm | 0.438″ / 11.13 mm | 94.55 kg/m | 13.124″ / 333.34 mm | 0.75″ / 19.05 mm | 158.11 kg/m | 12.5″ / 317.5 mm |

16″ | 400 mm | 16″ / 406.4 mm | 0.5″ / 12.7 mm | 123.31 kg/m | 15″ / 381 mm | 0.844″ / 21.44 mm | 203.54 kg/m | 14.312″ / 363.52 mm |

18″ | 450 mm | 18″ / 457 mm | 0.562″ / 14.27 mm | 155.81 kg/m | 16.897″ / 428.46 mm | 0.938″ / 23.83 mm | 254.57 kg/m | 16.124″ / 409.34 mm |

20″ | 500 mm | 20″ / 508 mm | 0.594″ / 15.09 mm | 183.43 kg/m | 18.812″ / 477.82 mm | 1.031″ / 26.19 mm | 311.19 kg/m | 17.938″ / 455.62 mm |

22″ | 550 mm | 22″ / 559 mm | 0.375″ / 9.53 mm | 129.14 kg/m | 21.25″ / 539.94 mm | 1.125″ / 28.58 mm | 373.85 kg/m | 19.75″ / 501.84 mm |

24″ | 600 mm | 24″ / 610 mm | 0.688″ / 17.48 mm | 255.43 kg/m | 22.624″ / 575.04 mm | 1.219″ / 30.96 mm | 442.11 kg/m | 21.562″ / 548.08 mm |

## Pipe Size Chart (26″ -48″ Nominal Bores)

Nominal Bore | Nominal Diameter | Outer Diameter | Standard Thickness | Standard Thickness Weight | Standard Thickness Internal Diameter | Extra Strong Thickness | Extra Strong Thickness Weight | Extra Strong Thickness Internal Diameter |

26″ | 650 mm | 26″ / 660 mm | 0.375″ / 9.53 mm | 152.88 kg/m | 25.25″ / 640.94 mm | 0.5″ / 12.7 mm | 202.74 kg/m | 25″ / 634.6 mm |

28″ | 700 mm | 28″ / 711 mm | 0.375″ / 9.53 mm | 164.86 kg/m | 27.25″ / 691.94 mm | 0.5″ / 12.7 mm | 218.71 kg/m | 27″ / 685.6 mm |

30″ | 750 mm | 30″ / 762 mm | 0.375″ / 9.53 mm | 176.85 kg/m | 29.25″ / 742.94 mm | 0.5″ / 12.7 mm | 234.68 kg/m | 29″ / 736.6 mm |

32″ | 800 mm | 32″ / 813 mm | 0.375″ / 9.53 mm | 188.83 kg/m | 31.25″ / 793.94 mm | 0.5″ / 12.7 mm | 250.65 kg/m | 31″ / 787.6 mm |

34″ | 850 mm | 34″ / 864 mm | 0.375″ / 9.53 mm | 200.82 kg/m | 33.25″ / 844.94 mm | 0.5″ / 12.7 mm | 266.63 kg/m | 33″ / 838.6 mm |

36″ | 900 mm | 36″ / 914 mm | 0.375″ / 9.53 mm | 212.57 kg/m | 35.25″ / 894.94 mm | 0.5″ / 12.7 mm | 282.29 kg/m | 35″ / 888.6 mm |

42″ | 1050 mm | 42″ / 1067 mm | 0.375″ / 9.53 mm | 248.53 kg/m | 41.25″ / 1047.94 mm | 0.5″ / 12.7 mm | 330.21 kg/m | 41″ / 1041.6 mm |

48″ | 1200 mm | 48″ / 1219 mm | 0.375″ / 9.53 mm | 284.25 kg/m | 47.25″ / 1199.94 mm | 0.5″ / 12.7 mm | 377.81 kg/m | 47″ / 1193.6 mm |