Seamless steel pipe sizes

The sizes of Seamless Steel pipes are jointly determined by the nominal diameter (NPS/DN) and the wall thickness grade (Schedule). Its actual outer diameter (OD) and inner diameter (ID) can be consulted in accordance with the ASME B36.10/B36.19 standard to meet different pressure and flow requirements.

The size range of seamless steel pipes

Outer diameter (OD) : The common NPS (nominal diameter) range is from ½ "to 36" (i.e., 21.3 mm - 914.4 mm).
Wall thickness (WT) : According to the pipe Schedule (wall thickness grade), it can range from approximately 2.11 mm to 60 mm, covering SCH10 to SCH160 and XXS (double thickening).

Characterization systems: NPS, DN, Schedule

NPS (Nominal Pipe Size) corresponds to DN (Nominal Diameter). For example: NPS ½ corresponds to DN 15, 1 "corresponds to DN 25, etc.
Schedule (SCH) indicates the wall thickness series, including SCH 5S/10S/10/20/30/40(S)/60/80(S)/100/120/140/160 and XXS.
The same NPS but different SCH correspond to the same outer diameter (OD), but the wall thickness, inner diameter (ID), and weight are different. For example: 4 "SCH 40 OD 114.3 mm wall thickness  6.02 mm SCH 80  8.56 mm.

A typical NPS-SCH counterpart example

NPS	OD	Wall Thickness		ID
in	in/mm	SCH 40	SCH 80	SCH 40	SCH 80
½	0.840″/21.3mm	0.109″/2.77mm	0.147″/3.73mm	≈0.622″／15.8mm	≈0.546″／13.9mm
¾	1.050″/26.7mm	0.113″/2.87mm	0.154″/3.91mm	≈0.824″／20.9mm	≈0.742″／18.9mm
1″	1.315″/33.4mm	0.133″/3.38mm	0.179″/4.55mm	≈1.049″／26.6mm	≈0.957″／24.3mm
2″	2.375″/60.3mm	0.154″/3.91mm	0.344″/8.74mm	≈2.067″／52.5mm	≈1.687″／42.9mm

There are mainly two common reference standards for the dimensions of seamless steel pipes:

ASME B36.10M: Dimensions standard for carbon steel and alloy steel pipes (seamless or welded), applicable to NPS ≤ 12 "(≈DN 300).
ASME B36.19M: The size standard for stainless steel pipes, Schedule is similar to B36.10, but there are slight differences in thickness under some NPS (such as 10S, 12S, etc.).

How to select the correct application

Determine the application and pressure requirements → Select the appropriate SCH (SCH 40 is often used for general purposes, while SCH 80 has higher pressure requirements).
Clarify the NPS (Nominal Size) → Then check the corresponding table of OD and WT.
Calculate the actual ID: ID ≈ OD - 2 × WT, which is used for the calculation of fluid flow and pressure drop.
Reference weight value: It can be estimated based on OD, WT, and material density, or directly obtained from a table (kg/m or lb/ft).

Read more： ERW carbon steel pipe sizes