Pipe Thickness Chart How to Calculate Wall Thickness for Different Applications

A pipe thickness chart for pipes comes in different sizes and schedules, so you can easily check and look into how thick the pipe wall actually is at any given size. This article gives you that chart in both millimetres and inches, then goes further than a simple lookup table. You will find the ASME B31.3 formula for calculating minimum wall thickness, a full worked example for a real pipe size, and guidance on how wall thickness is approached across oil and gas, chemical processing, power generation, marine and pharmaceutical applications.

What Is Pipe Wall Thickness? 

The thickness of the wall of the pipe is the distance from the outside surface of the pipe to the inside of the bore of the pipe. Wall Thickness is determined by taking the difference between the Outside Diameter (OD) and the Inside Diameter (ID) of the product divided by 2. The wall thickness is a significant pipe dimension that relates to pressure capacity, weight, cost, corrosion allowance and service life. A thicker wall will generally be more resistant to the internal pressure, and will also be more able to withstand corrosion and/or erosion during service. If the wall thickness is increased while the outside diameter is kept the same, though, the flow area inside the wall will decrease, which will also decrease the capacity. This will raise the speed of the fluid and reduce the pressure. The thickness of pipes should then be determined not only on the basis of the thickness that is currently available, but also based on the operating conditions, applicable standards, flow requirements, corrosion allowance, pressure and temperature.

Pipe Thickness Chart: Wall Thickness by NPS and Schedule 

Pipes Thickness Chart Inch Dimension Reference (SCH 40 and SCH 80) 

Pipe Schedule Explained: SCH 5S, 10S, 40, 80, 160 and XXS

The North American sizing term is NPS (nominal pipe size) and its metric equivalent is DN (diamètre nominal) as used in European and international specifications. It is not the actual outside diameter, but a reference value; the actual OD is a fixed value found in the chart above, in relation to the NPS or DN value. To understand the relationship between NPS and OD for the entire size range in detail, please consult our steel pipe size chart.

ASME B36.19M defines stainless steel pipe schedules with the “S” suffix such as SCH 10S, 40S, etc. Schedules that do not include the S, like SCH 40, 80 and 160, are used with carbon and alloy steel pipe and follow ASME B36.10M. The numbers are aligned at NPS 1/2 to NPS 8 (SCH 10 equals 10S, etc.), but this is not always true for all sizes, so please check the chart, don’t assume.

Also, the old terminology STD (standard), XS (extra strong) and XXS (double extra strong) will be found on some older drawings and on some supplier catalogues. In this size range, STD will be 40 and XS will be 80. But XXS is not just “thicker than SCH 160”, however; NPS 8 shows NPS 8’s thickness is 22.23 mm, while SCH 160’s thickness is 23.01 mm, so SCH 160 is the thicker of the two. Never rely on schedule names, always refer to the actual thickness value in the chart.

How to Calculate Pipe Wall Thickness (ASME B31.3 Formula)

The pipe wall thickness formula used under ASME B31.3, the code governing process piping, is:

t = P x D / (2 x (S x E x W + P x Y))

Calculating minimum wall thickness follows five steps:

1. Collect your inputs: design pressure, outside diameter, design temperature, and whether the pipe is seamless or welded.
2. Find the allowable stress S for your material at the design temperature, from the applicable ASME B31.3 stress table.
3. Calculate t using the formula above.
4. Add your allowances (corrosion, mechanical, erosion) to t, giving the minimum required thickness.
5. Divide by 0.875 to account for the standard 12.5% mill under-tolerance, then choose the next schedule at or above that value from the chart.

This formula applies to straight pipe under internal pressure where t is less than D divided by 6. It is a design formula, not a substitute for engineering judgement: final wall thickness selection must follow the governing project code and be reviewed by a qualified piping engineer. Other codes, such as ASME B31.1 for power piping or B31.4 and B31.8 for pipelines, use similar equations with different factors and stress tables. The weld joint quality factor E is discussed in more detail in our seamless vs welded steel pipe comparison.

Pipe Wall Thickness for Different Applications

The right wall thickness depends heavily on what the pipe is actually being asked to do. Here is how wall thickness is typically approached across the industries we supply into.

Stainless Steel Pipe Wall Thickness

Stainless steel pipe wall thickness generally follows ASME B36.19M’s S-schedules, which frequently run lighter than the equivalent carbon steel schedule at the same NPS, since austenitic stainless steel typically carries a higher allowable stress than plain carbon steel at moderate temperatures. Our stainless steel pipes and tubes range and our 304 stainless steel pipe page cover the grades most often specified at SCH 10S and 40S.

Nickel Alloys: Inconel, Hastelloy, Monel

Nickel alloys are usually chosen for their resistance to a specific aggressive media rather than for raw mechanical strength, which means the corrosion allowance, not the pressure calculation alone, often ends up driving the final wall thickness. Our Inconel pipes and tubes, Hastelloy pipes and tubes and Monel pipes and tubes ranges cover the alloys most commonly specified for these duties.

Duplex and Super Duplex

Duplex and super duplex steels combine high mechanical strength with strong resistance to chloride pitting and stress corrosion, which can allow a thinner wall than an austenitic stainless grade would need at the same design pressure, always subject to the governing code’s stress tables. See our duplex 2205 pipe and tube and super duplex pipes and tubes ranges.

Titanium

Titanium’s strength-to-weight ratio can allow a lighter wall for a given pressure rating compared with steel, though the comparison depends heavily on the specific grade, temperature and design code involved. Our titanium pipes and tubes range and our titanium vs stainless steel pipe strength comparison go into this in more depth.

Common Mistakes When Choosing Pipe Wall Thickness

• Assuming SCH 40 is the same thickness at every pipe size, when it actually varies significantly by NPS.
• Choosing a schedule straight from the chart without first calculating the actual pressure requirement.
• Ignoring corrosion allowance and specifying only the bare pressure design thickness.
• Forgetting the 12.5% mill under-tolerance when converting a calculated minimum wall into an order thickness.
• Mixing ASME B36.10M (carbon and alloy steel) and B36.19M (stainless) values when specifying stainless pipe, when the two tables are not always identical outside the common size range.
• Ordering tube by NPS and schedule, when tube is specified by actual OD and wall thickness instead.
• Over-specifying wall thickness on costly alloys such as Inconel or Hastelloy when the calculated requirement, plus a reasonable allowance, would suffice.

How to Order Pipe by Wall Thickness: RFQ Checklist

Send the following details with any pipe or tube enquiry, so we can quote accurately the first time:

• Material and grade
• Governing standard, for example ASTM A312
• Seamless or welded
• NPS and schedule, or OD and wall thickness in mm, depending on pipe or tube
• Length
• Quantity
• Documentation required (MTC, EN 10204 3.1 or 3.2)
• Inspection requirements
• Delivery location

Stellar Alloys supplies material with MTC and heat-number traceability, custom sizes and cut lengths, and full export documentation. See our global export guide for shipping and documentation details, or request a quote directly with your specification.

Conclusion:

Choosing the right pipe wall thickness comes down to three steps: read the pipe thickness chart to see what standard schedules are available, calculate the minimum wall your design pressure and material actually require, and match that figure to the application, factoring in corrosion allowance and the governing code. Skipping straight to a schedule without the calculation, or ignoring the tolerance and corrosion margin, are the two mistakes that cause the most rework later. If you would like help confirming wall thickness for a specific project, request a quote and our team will work through it with you.