This article focuses on the Pipe OD Chart and the sizing systems behind it. In the steel pipe industry, pipe outside diameter (OD) is not simply a matter of standard dimensions. It is closely related to NPS, DN, ASME B36.10M, ASME B36.19M, Metric OD, and API pipe sizing systems.
Today, ALLLAND will break down these different pipe sizing systems and provide a detailed explanation of pipe outside diameters.
What Is a Pipe OD Chart?
Pipe OD Chart stands for Pipe Outside Diameter Chart. Here, OD primarily refers to the outside diameter of the pipe, measured across the outermost edges of the pipe wall.
The following is an example of pipe diameter dimensions:
| NPS | Pipe OD |
| 1/2″ | 21.3 mm |
| 1″ | 33.4 mm |
| 2″ | 60.3 mm |
| 3″ | 88.9 mm |
| 4″ | 114.3 mm |
| 6″ | 168.3 mm |
| 8″ | 219.1 mm |
| 10″ | 273.1 mm |
| 12″ | 323.9 mm |
Note: NPS refers to the Nominal Pipe Size. NPS 2 does not mean that the pipe has an outside diameter of 2 inches. The actual outside diameter of NPS 2 pipe is 60.3 mm (2.375 inches).
Pipe OD Chart Systems
Pipe outside diameter (OD) is an important parameter in pipe manufacturing and procurement. Different countries and regions may use different pipe sizing and outside diameter systems. Below, we will introduce several important pipe OD sizing systems and provide the corresponding Pipe OD Charts for your reference.
NPS / ASME System
The NPS / ASME system is an important pipe sizing system widely used in North America and international projects. It is primarily based on ASME B36.10M.
One important characteristic of this system is that when NPS is 14 inches or larger, NPS is approximately equal to the actual pipe OD in inches. However, this relationship does not apply to smaller pipe sizes.
For detailed dimensions, please refer to the table below:
| NPS | OD inch | OD mm |
| 1/2″ | 0.84 | 21.3 |
| 1″ | 1.315 | 33.4 |
| 2″ | 2.375 | 60.3 |
| 3″ | 3.5 | 88.9 |
| 4″ | 4.5 | 114.3 |
| 6″ | 6.625 | 168.3 |
| 8″ | 8.625 | 219.1 |
| 10″ | 10.75 | 273.1 |
| 12″ | 12.75 | 323.9 |
| 16″ | 16 | 406.4 |
| 20″ | 20 | 508 |
| 24″ | 24 | 610 |
OD and Schedule Size Chart System
Schedule does not represent the pipe outside diameter (OD); it refers to the pipe wall thickness. In this sizing system, Schedule is often combined with NPS (Nominal Pipe Size) and serves as a fundamental specification for steel pipe purchasing. NPS determines the pipe outside diameter, while Schedule determines the wall thickness.
Below are some common pipe size combinations of NPS and Schedule for reference. For a more complete chart, please view the full Schedule Dimensions Chart.
| NPS | OD | SCH 40 WT | SCH 80 WT |
| 2″ | 60.3 mm | 3.91 mm | 5.54 mm |
| 3″ | 88.9 mm | 5.49 mm | 7.62 mm |
| 4″ | 114.3 mm | 6.02 mm | 8.56 mm |
| 6″ | 168.3 mm | 7.11 mm | 10.97 mm |
| 8″ | 219.1 mm | 8.18 mm | 12.70 mm |
| 10″ | 273.1 mm | 9.27 mm | 12.70/15.09 mm |
Metric Pipe OD Chart System
The Metric OD system is also an important pipe sizing system. It is a typical Outside Diameter × Wall Thickness (OD × WT) sizing system and is commonly used for steel pipe procurement in Europe, Australia, and Asia.
API / OCTG Chart System
For pipes manufactured according to API standards, the commonly used dimensional format is OD × WT. However, for OCTG (Oil Country Tubular Goods), the pipe cannot be fully specified for manufacturing and procurement based on OD and WT alone. The key specifications typically include Nominal Size + Weight + Grade.
For example, if a buyer requests 7″ 29 lb/ft P110 OCTG pipe, the 7″ does not mean that the actual outside diameter (OD) is 7 inches. Instead, it refers to the Nominal Size = 7 inches. The actual outside diameter needs to be determined according to the applicable OCTG dimensional table.
It is important to note that Nominal Size is not the same as NPS. These are two different sizing concepts.
Below, we compare some common NPS and OCTG Nominal Sizes for reference.
| NPS | Nominal Size | Actual OD |
| 1/2″ | 1/2 inch | 21.3 mm |
| 1″ | 1 inch | 33.4 mm |
| 2″ | 2 inch | 60.3 mm |
| 3″ | 3 inch | 88.9 mm |
| 4″ | 4 inch | 114.3 mm |
| 6″ | 6 inch | 168.3 mm |
| 8″ | 8 inch | 219.1 mm |
| 10″ | 10 inch | 273.1 mm |
| 12″ | 12 inch | 323.9 mm |
| 16″ | 16 inch | 406.4 mm |
| 20″ | 20 inch | 508.0 mm |
| 24″ | 24 inch | 610.0 mm |
If you need a detailed OCTG Size Chart, please click the link below to view it.
JIS Pipe OD Charts System
JIS (Japanese Industrial Standards) is a pipe sizing system used in Japan. Its pipe outside diameters are not completely identical to those specified by ASME, and there are some dimensional differences between the two systems. The table below lists some of these differences for reference.
| Comparison Item | ASME / NPS | JIS | Difference |
| Nominal Size | 1½” | — | — |
| Outside Diameter | 48.3 mm | 48.6 mm | 0.3 mm |
| Nominal Size | 2″ | — | — |
| Outside Diameter | 60.3 mm | 60.5 mm | 0.2 mm |
| Nominal Size | 3″ | — | — |
| Outside Diameter | 88.9 mm | 89.1 mm | 0.2 mm |
| Nominal Size | 4″ | — | — |
| Outside Diameter | 114.3 mm | 114.3 mm | 0 mm |
| Nominal Size | 6″ | — | — |
| Outside Diameter | 168.3 mm | 165.2 mm | 3.1 mm |
| Nominal Size | 8″ | — | — |
| Outside Diameter | 219.1 mm | 216.3 mm | 2.8 mm |
The Pipe OD Charts mentioned above may vary slightly depending on the sizing system and applicable standard. In the steel pipe industry, it is important to understand these differences in order to select and manufacture the correct pipe dimensions.
We hope this article provides you with a useful reference for understanding different Pipe OD Chart systems. If you are looking for reliable steel pipe for your project, please feel free to contact ALLLAND for your steel pipe requirements.
NPS vs OD
| NPS | OD inch | OD mm |
| 1/8″ | 0.405 | 10.3 |
| 1/4″ | 0.54 | 13.7 |
| 3/8″ | 0.675 | 17.1 |
| 1/2″ | 0.84 | 21.3 |
| 3/4″ | 1.05 | 26.7 |
| 1 | 1.315 | 33.4 |
| 1-1/4″ | 1.66 | 42.2 |
| 1-1/2″ | 1.9 | 48.3 |
| 2″ | 2.375 | 60.3 |
| 12-1/2″ | 2.875 | 73 |
| 3″ | 3.5 | 88.9 |
| 4″ | 4.5 | 114.3 |
| 6″ | 6.625 | 168.3 |
| 8″ | 8.625 | 219.1 |
| 10″ | 10.75 | 273.1 |
| 12″ | 12.75 | 323.9 |
NPS to OD Converter — Click the link below to use the converter: NPS to OD Converter
