How Thick Is Schedule 40 Pipe? Wall Thickness Chart, Standards, and Selection Guide

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How thick is schedule 40 pipe? In the field of pipeline engineering, it is very important to choose the right steel pipe. This is one of the most common technical questions in piping projects. Among them, Schedule 40 pipe is a common pipe specification. For example, 6 Schedule 40 pipe, 2 schedule 40 pipe, 4 inch schedule 40 pipe.

The answer is straightforward but often misunderstood: Schedule 40 pipe thickness depends on the nominal pipe size (NPS). It is not one fixed wall value.

Schedule 40 is defined by internationally recognized standards and is widely used because it balances strength, weight, weldability, and cost. Below, you’ll find the exact wall thickness values, the governing standards, engineering considerations, and what procurement teams should confirm before placing an order.

How Thick Is Schedule 40 Pipe?

There is no single thickness for Schedule 40.

Wall thickness increases as pipe diameter increases to maintain hoop stress resistance under internal pressure.

SCH 40 pipe thickness in mm, For example:

1″ Schedule 40 thickness = 0.133 inch (3.38 mm)
2″ Schedule 40 thickness = 0.154 inch (3.91 mm)
6″ Schedule 40 thickness = 0.280 inch (7.11 mm)
12″ Schedule 40 thickness = 0.406 inch (10.31 mm)

The outside diameter remains constant for a given NPS. Only the wall thickness changes between schedules.

Schedule 40 Pipe Wall Thickness Chart (Common Sizes)

SCH 40 Pipe Thickness in mm- Pipe Schedule Chart

Below are commonly requested sizes for carbon steel pipe under ASME B36.10M:

Schedule 40 Wall Thickness (NPS 1/2″-12″) Chart

NPS	OD (inch)	Wall Thickness (inch)	Wall Thickness (mm)
1/2″	0.840	0.109	2.77
1″	1.315	0.133	3.38
2″	2.375	0.154	3.91
3″	3.500	0.216	5.49
4″	4.500	0.237	6.02
6″	6.625	0.280	7.11
8″	8.625	0.322	8.18
12″	12.750	0.406	10.31

Thickness increases with diameter because larger pipes experience higher circumferential (hoop) stress under internal pressure.

Schedule 40 Pipe Thickness By Size

Schedule 40 pipe thickness in mm:

2 Inch Schedule 40 Pipe Thickness

OD = 2.375″

Wall Thickness = 0.154″

3.91 mm

This size is widely used in fire protection systems, water pipelines, compressed air systems, and structural applications.

4 Inch Schedule 40 Pipe Thickness

OD = 4.500″

Wall Thickness = 0.237″

6.02 mm

This size is commonly used in municipal water systems, industrial piping, and oil and gas projects.

6 Inch Schedule 40 Pipe Thickness

OD = 6.625″

Wall Thickness = 0.280″

7.11 mm

This size is frequently selected for water transportation, infrastructure projects, and process piping systems.

8 Inch Schedule 40 Pipe Thickness

OD = 8.625″

Wall Thickness = 0.322″

8.18 mm

This size is widely used in water treatment plants, industrial facilities, and transmission pipelines.

12 Inch Schedule 40 Pipe Thickness

OD = 12.750″

Wall Thickness = 0.406″

10.31 mm

This size is often used in large water transmission systems, energy projects, and infrastructure construction.

PANDAPIPE Experience With Schedule 40 Pipe Orders

Based on PANDAPIPE export data, more than 60% of standard carbon steel pipe orders are supplied in Schedule 40 wall thickness because it offers a practical balance between strength, availability, and cost.

Application Industry	Estimated Share of Orders	Most Popular Pipe Size	Common Standard
Water Supply Projects	35%	4″–12″	ASTM A53 Grade B
Structural Construction	30%	4″–20″	ASTM A500
Fire Protection Systems	15%	2″–8″	ASTM A53 Grade B
Oil & Gas Projects	10%	2″–16″	API 5L
Mechanical Engineering	10%	1″–6″	ASTM A53 / ASTM A106

Key Insight from PANDAPIPE:
Based on PANDAPIPE export experience, Schedule 40 accounts for more than 60% of carbon steel pipe orders because it provides sufficient mechanical strength for most applications while maintaining a lower cost than Schedule 80.

What Does Schedule 40 Actually Mean?

Schedule Refers to Wall Thickness, Not Pressure

Many buyers assume Schedule 40 defines pressure rating. It does not.

In the NPS system:

Outside Diameter (OD) is fixed.
Wall thickness varies by schedule number.
Inside Diameter (ID) decreases as wall thickness increases.

For example, a 2″ Schedule 40 pipe and a 2″ Schedule 80 pipe have the same OD. However, Schedule 80 has a thicker wall and smaller ID.

This standardization ensures compatibility with flanges, fittings, valves, and welded connections.

Which Standards Define Schedule 40 Dimensions?

ASME B36.10M Thickness& Specification

Schedule 40 Piping specifications are classified and labeled according to American standard ASME B36.10M. How thick is Schedule 40 pipe? Its wall thickness value is not fixed, and is generally calculated according to the outside diameter and nominal pressure (PN) of the pipeline.

For example, a pipe with an outer diameter of 168.3mm has a Schedule 40 wall thickness of 7.11mm. Schedule 40 steel pipe with a 1/2 inch diameter has a minimum wall thickness of approximately 0.133 inches (approximately 3.38mm). On the other hand, the length and material of Schedule 40 pipeline will also have a great impact on wall thickness and mechanical properties.

Schedule 40 dimensions are governed by:

ASME B36.10M – Welded and seamless wrought steel pipe
ASME B36.19M – Stainless steel pipe (Sch 40S)

These standards define OD and wall thickness to ensure global interchangeability.

If your specification references ASTM A53, ASTM A106, or API 5L, the dimensional schedule still follows ASME B36.10M.

Why Engineers Frequently Select Schedule 40

Schedule 40 is often referred to as “Standard Weight (STD)” for sizes up to NPS 10.

It is widely selected because it offers:

1. Balanced Strength-to-Weight Ratio

For water, compressed air, fire systems, and general industrial service, Schedule 40 typically provides adequate safety margin without unnecessary structural load.

2. Cost Efficiency

Schedule 40 is mass-produced globally. Higher production volume generally means shorter lead times and stable pricing compared to heavier schedules.

3. Practical Weldability

The wall thickness allows standard welding procedures without excessive bevel preparation or multi-pass welding required by heavier schedules.

Typical Applications of Schedule 40 Pipe

Schedule 40 is commonly used in:

Municipal water distribution
HVAC chilled water lines
Fire sprinkler systems
Compressed air systems
General industrial utilities
Structural supports
Low-to-medium pressure oil and gas transport

For high-pressure steam, high-temperature service, or corrosive chemical systems, engineers often select Schedule 80 or higher to allow additional corrosion margin.

Critical Technical Clarification: Schedule ≠ Pressure Rating

This is a frequent source of procurement errors.

Allowable working pressure depends on:

Material grade (e.g., ASTM A53, ASTM A106, API 5L)
Wall thickness
Operating temperature
Corrosion allowance
Design safety factor

For example:

A Schedule 40 pipe manufactured under ASTM A53 Grade B does not have the same pressure capacity as a Schedule 40 pipe under API 5L X52.

Schedule defines thickness.
Material grade defines strength.

Pressure design typically follows formulas such as Barlow’s formula, using allowable stress values defined in ASME design codes.

How To Calculate Pressure Rating Of Schedule 40 Pipe

P = Pressure
S = Allowable Stress
t = Wall Thickness
D = Outside Diameter

Manufacturing Tolerance and Inspection

According to ASTM standards, wall thickness tolerance generally permits up to 12.5% under the nominal wall thickness.

This means actual thickness may be slightly lower than the nominal value.

For critical projects, it is recommended to specify:

Minimum wall thickness requirement
Hydrostatic testing
Third-party inspection
Mill Test Certificate (EN 10204 3.1)

Clear technical specifications reduce compliance disputes and project delays.

Schedule 40 vs Schedule 80 – When to Upgrade

Factor	Schedule 40	Schedule 80
Wall Thickness	Medium	Thick
Pressure Capacity	Moderate	Higher
Weight	Lighter	Heavier
Welding Effort	Standard	Increased
Cost	Lower	Higher

As a general engineering guideline of how to choose schedule 40 vs 80 steel pipe:

If design pressure is moderate and corrosion is controlled, Schedule 40 is usually sufficient.

If operating pressure, temperature, or corrosion allowance increases, engineers often choose Schedule 80 for additional safety margin.

How to Select the Correct Schedule Before Sending an RFQ

Before requesting a quotation, confirm the following:

1. Design Pressure and Temperature

Start with engineering calculation, not price comparison.

2. Material Grade

Common grades include ASTM A53, ASTM A106, and API 5L. Each has different mechanical properties.

3. Pipe Manufacturing Type

Seamless (SMLS) for higher pressure or critical systems.
ERW for cost-efficient general applications.

4. End Preparation

Plain End (PE), Beveled End (BE), or Threaded & Coupled (T&C).

5. Surface Treatment

Black lacquered, galvanized, FBE coating, or 3LPE coating.

Clear RFQ details significantly reduce delivery errors and rework costs.

How Thick Is Schedule 40 Pipe – Need Verified Supply?

If you are specifying how thick is schedule 40 pipe for a tender or industrial project, we can assist with technical verification and compliant supply.

At PANDAPIPE, we supply:

Schedule 40 carbon steel and stainless steel pipes
Seamless and ERW options
Full MTC traceability
Export-compliant packaging
Custom cutting and coating services

Our team supports project-based RFQs with dimensional confirmation and compliance review.

Contact us today to receive a detailed quotation and technical support for your Schedule 40 pipe requirements.

FAQs

1. How thick is 2 inch Schedule 40 pipe?

The wall thickness is 0.154 inch (3.91 mm).

2. Is Schedule 40 the same as Standard Weight (STD)?

For sizes up to NPS 10, Schedule 40 is generally equivalent to STD. Larger sizes may differ.

3. Can Schedule 40 handle high-pressure gas?

Only if engineering calculations confirm allowable stress meets safety requirements.

4. Does Schedule 40 mean high pressure?

No. It is a dimensional classification, not a pressure rating.

5. Is Schedule 40 stronger than Schedule 10?

Yes, because it has a thicker wall.

6. What material is Schedule 40 pipe made from?

Common materials include carbon steel (ASTM A53, A106) and stainless steel (Sch 40S).

7. Does Schedule 40 affect welding procedures?

Yes. Thicker walls require more welding input and inspection.

8. How do I verify compliance?

Request a Mill Test Certificate and confirm conformity to ASME and ASTM standards.

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Mu Shuang

February 24, 2026

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