Steel Tube Size Chart

Selecting the correct steel pipe size is essential for ensuring the safety, performance, and cost-efficiency of any construction, industrial, or pipeline project. Whether you are designing a structural framework, transporting fluids, or installing mechanical systems, understanding pipe dimensions, wall thickness, and pressure ratings helps you choose the most suitable product.

This guide provides a practical overview of steel pipe sizes, including Nominal Pipe Size (NPS), Outside Diameter (OD), Wall Thickness, Pipe Schedule, and DN conversions. It also explains how different pipe dimensions influence strength, flow capacity, and application requirements.

At TJMC Steel, we supply a complete range of steel pipe products, including Seamless Steel Pipes, ERW Steel Pipes , Galvanized Steel Pipes, Square and Rectangular Steel Tubes for customers worldwide.

Steel Pipe Size Standards

Steel pipes are manufactured according to internationally recognized standards to ensure compatibility, safety, and performance across different industries. Depending on the project requirements, the following standards are commonly used:

• ASTM A53 – General-purpose steel pipes

• ASTM A106 – Seamless carbon steel pipe for high-temperature service

• ASTM A500 – Structural steel tubing

• API 5L – Line pipe for oil and gas transmission

• EN 10219 – Cold-formed structural hollow sections

• EN 10210 – Hot-finished structural hollow sections

• JIS G3454 / G3456 – Japanese carbon steel pipe standards

These standards define dimensions, mechanical properties, testing methods, and manufacturing tolerances. Before selecting a steel pipe, engineers should always verify that the required standard complies with the project's specifications and local regulations.

Steel Pipe Size Chart 

The following table shows the most commonly used Nominal Pipe Sizes (NPS), corresponding outside diameters, and typical wall thicknesses for Schedule 40 and Schedule 80 pipes.

The table above lists standard reference dimensions. Additional sizes, schedules, and customized specifications are available upon request.

If your project requires customized lengths, heavy-wall pipes, or special material grades, please contact TJMC Steel for technical assistance.

NPS vs DN Conversion Guide

One of the most common questions from international buyers is the difference between NPS and DN.

• NPS (Nominal Pipe Size) is the North American pipe sizing system defined by ASME and ASTM standards.

• DN (Diamètre Nominal) is the international metric designation commonly used in Europe and many other countries.

Although NPS and DN are approximately equivalent, neither value represents the actual outside diameter of the pipe. The outside diameter remains constant for a given NPS, while the internal diameter changes according to the selected pipe schedule.

For example:

Understanding this relationship is essential when selecting fittings, valves, flanges, and other pipeline components.

For structural applications, buyers may also consider Square Steel Tubes or Rectangular Steel Tubes , depending on the design requirements.

Understanding Steel Pipe Schedule

When selecting a steel pipe, the outside diameter is only part of the specification. Another critical factor is the pipe schedule, which determines the wall thickness of the pipe. Pipes with the same outside diameter can have different wall thicknesses depending on the selected schedule, directly affecting pressure resistance, weight, and service life.

The most commonly used schedules include:

Among these, Schedule 40 and Schedule 80 are the most widely used worldwide.

Schedule 40 pipes offer an excellent balance between strength, weight, and cost, making them suitable for most commercial and structural projects. Schedule 80 pipes feature thicker walls and greater pressure resistance, making them the preferred choice for demanding industrial environments.

When specifying a steel pipe, always consider both the Nominal Pipe Size (NPS) and the Schedule, as these two parameters together determine the pipe's actual dimensions and performance.

How to Choose the Right Steel Pipe Size

Selecting the appropriate steel pipe involves more than simply choosing a diameter. Engineers and buyers should evaluate several technical factors to ensure the pipe meets both performance and budget requirements.

1. Application

The intended use of the pipe is the first consideration.

For example:

• Structural columns and frames generally prioritize strength and rigidity.

• Water transmission systems focus on flow capacity and corrosion resistance.

• Oil and gas pipelines require pressure resistance and compliance with industry standards.

• Mechanical fabrication may prioritize dimensional accuracy and ease of machining.

Different applications often require different manufacturing processes and standards.

2. Outside Diameter and Wall Thickness

Outside diameter determines compatibility with fittings, flanges, and valves, while wall thickness influences:

• Internal flow area

• Pressure rating

• Structural strength

• Overall pipe weight

Choosing a thicker wall increases durability but also adds weight and cost. Selecting the correct balance is essential for efficient project design.

3. Material and Manufacturing Method

Different manufacturing methods provide different performance characteristics.

TJMC Steel supplies:

• Seamless Steel Pipes for high-pressure and high-temperature applications.

• ERW Steel Pipes  for structural and general industrial use.

• Galvanized Steel Pipes  for outdoor environments requiring corrosion protection.

Each product offers unique advantages depending on the service conditions.

4. Surface Protection

For projects exposed to moisture, chemicals, or outdoor weather, galvanized or coated pipes can significantly extend service life and reduce maintenance costs.

Depending on the project requirements, surface finishes may include:

• Black steel

• Hot-dip galvanized

• Pre-galvanized

• Painted

• Epoxy-coated

Selecting the appropriate surface treatment improves long-term performance and lifecycle value.

5. Applicable Standards

Always verify that the selected pipe complies with the engineering specification.

Common standards include:

• ASTM

• API

• EN

• JIS

• DIN

Material certificates and inspection reports should also be considered when purchasing structural or pressure-service steel pipes.