Steel Pipe Wall Thickness Chart: SCH, mm, Inch and Gauge Explained

A practical guide for buyers comparing Sch 40, Sch 80 and direct thickness notation

Pipe wall thickness must be specified together with nominal pipe size (NPS) or outside diameter (OD). SCH 40 and SCH 80 are wall-thickness series, not fixed millimeter values or pressure ratings. Use the tables below to compare schedule, millimeter, inch and gauge notation before preparing a pipe order.

For the same NPS, compare the specified SCH 40 or SCH 80 wall thickness, then confirm the material standard, grade and manufacturing route. Both seamless steel pipe and ERW steel pipe may be supplied in scheduled sizes, subject to the applicable standard and the confirmed OD/wall combination.

A dimension such as 114.3 x 6.02 mm states outside diameter x nominal wall thickness. For an unambiguous quotation, also specify the grade, standard, length, quantity and wall-thickness tolerance. Do not use nominal diameter as a substitute for actual outside diameter.

A thicker wall alone does not establish allowable working pressure. The design basis also depends on material, temperature, manufacturing tolerances, corrosion allowance and the governing code. For API 5L line pipe, state the grade and PSL as well as the dimensions.

Need dimensions for a specific size? Use the pipe schedule chart for size-by-size reference rows. This guide explains how to read and specify the wall thickness; gauge values must be checked against the named gauge system.

Table 1. Common Global Wall Thickness Expression Methods

Table 2. Selected NPS 4 Wall Thicknesses

Table 3. Same Schedule, Different Thickness by Pipe Size

Table 4. Common BWG Reference Values

Table 5. How Buyers Commonly Write Wall Thickness in Orders

Page scope: Use this guide to express wall thickness by Schedule, millimeter, inch or gauge and to write an unambiguous purchase description. Use the Size Chart for NPS/DN/OD conversion, the Schedule Chart for dimension rows, and the Weight guide for kg/m and lb/ft.

Related Reading

· Pipe Schedule Chart: Steel Pipe Dimensions and Wall Thickness

· Steel Pipe Tolerance Guide: What Buyers Must Check Before Order, During Production and Before Shipment

· Steel Pipe Weight: Formula, Reference Chart and Shipping Estimates

· Steel Pipe Specification Review Before Production: How We Avoid Wrong Material or Wrong Standard

References & Sources

1.ASME —B36.10M — Welded and Seamless Wrought Steel Pipe. Primary dimensional reference for NPS, outside diameter, wall thickness and schedule designations for wrought steel pipe.

2.ASME —Product Standardization and Specifications. Explains the role of B36 dimensional standards, including B36.10M and B36.19M, in pipe standardization.

3.NIST —Guide for the Use of the International System of Units (SI). Supports consistent conversion and presentation of millimetres, inches and other measurement units.

4.ASTM International —ASTM A106/A106M — Seamless Carbon Steel Pipe for High-Temperature Service. Shows how a material specification references pipe dimensions, permitted variations and ordering requirements rather than replacing the dimensional standard.

5.American Petroleum Institute —API Specification 5L, 47th Edition. Provides the line-pipe specification context for dimensions, tolerances, product specification levels and ordering information.

Applicability note: Schedule is a dimensional designation, not a direct pressure rating and not an interchangeable substitute for a specified wall thickness. Final selection requires the governing design code, material grade, corrosion allowance, tolerance, temperature and project specification.