When working with plumbing, construction, or mechanical systems, pipes are everywhere. But not all pipes are created equal—some are thicker, some thinner, and that difference matters when handling pressure, durability, and overall performance. That’s where the pipe schedule chart comes in.
The term pipe schedule simply refers to the thickness of the pipe wall. It doesn’t change the outer diameter (OD), but it changes the inner diameter (ID), which affects flow capacity and strength. Understanding pipe schedules can help you select the right type of pipe for your project, whether it’s for water supply, gas lines, oil pipelines, or industrial use.
In this guide, we will explore what pipe schedule means, why it’s important, how to read a pipe schedule chart, and provide examples with metric and imperial measurements.
What is Pipe Schedule?
The word schedule in piping does not mean time—it’s a technical term developed by the American Society of Mechanical Engineers (ASME). A pipe schedule (often abbreviated as SCH) is a standard that shows the wall thickness of pipes.
For example:
Schedule 40 pipe has a medium wall thickness and is the most common type.
Schedule 80 pipe has a thicker wall, making it stronger and better for high-pressure applications.
Schedule 160 pipe is extremely thick and is used in specialized heavy-duty industries.
Even though the outer diameter (OD) of a pipe stays the same for a given nominal pipe size (NPS), the inner diameter (ID) shrinks as the schedule number increases.
Why is Pipe Schedule Important?
Pressure Handling – A thicker wall (higher schedule) means the pipe can handle more internal pressure.
Durability – Heavy-duty schedules resist cracking, corrosion, and wear better.
Flow Capacity – A thinner wall (lower schedule) means a larger internal diameter and better fluid flow.
Safety – Choosing the wrong schedule can lead to leaks, bursts, or failures.
Pipe Schedule Number Formula
The schedule number is calculated using this formula:
Schedule Number=1000×PSSchedule Number = \frac{1000 \times P}{S}
Where:
P = Internal pressure (psi)
S = Allowable stress (psi) of the material
This formula shows why different schedules exist—higher pressures require stronger (thicker) pipes.
Common Pipe Schedules
The most commonly used pipe schedules are:
Schedule 10 (SCH 10): Thin-walled, often used in low-pressure applications.
Schedule 40 (SCH 40): Standard thickness, widely used for plumbing and general applications.
Schedule 80 (SCH 80): Thicker and stronger, used in industrial and high-pressure systems.
Schedule 160 (SCH 160): Very thick, heavy-duty use.
XXS (Double Extra Strong): Special applications requiring maximum strength.
Pipe Schedule Chart (Imperial)
Here’s a simplified chart of some common nominal pipe sizes (NPS) with OD and wall thickness values for Schedule 40 and 80:
| Nominal Pipe Size (NPS) | Outside Diameter (OD) | SCH 40 Wall Thickness | SCH 80 Wall Thickness |
|---|---|---|---|
| 1/2 inch | 0.84 in (21.3 mm) | 0.109 in (2.77 mm) | 0.147 in (3.73 mm) |
| 1 inch | 1.315 in (33.4 mm) | 0.133 in (3.38 mm) | 0.179 in (4.55 mm) |
| 2 inch | 2.375 in (60.3 mm) | 0.154 in (3.91 mm) | 0.218 in (5.54 mm) |
| 4 inch | 4.5 in (114.3 mm) | 0.237 in (6.02 mm) | 0.337 in (8.56 mm) |
| 6 inch | 6.625 in (168.3 mm) | 0.28 in (7.11 mm) | 0.432 in (10.97 mm) |
| 8 inch | 8.625 in (219.1 mm) | 0.322 in (8.18 mm) | 0.5 in (12.7 mm) |
Pipe Schedule Chart (Metric Conversion)
For engineers and users outside the U.S., the following shows the same data in millimeters:
| Nominal Pipe Size (DN) | Outside Diameter (mm) | SCH 40 Wall Thickness | SCH 80 Wall Thickness |
|---|---|---|---|
| DN 15 (1/2 inch) | 21.3 mm | 2.77 mm | 3.73 mm |
| DN 25 (1 inch) | 33.4 mm | 3.38 mm | 4.55 mm |
| DN 50 (2 inch) | 60.3 mm | 3.91 mm | 5.54 mm |
| DN 100 (4 inch) | 114.3 mm | 6.02 mm | 8.56 mm |
| DN 150 (6 inch) | 168.3 mm | 7.11 mm | 10.97 mm |
| DN 200 (8 inch) | 219.1 mm | 8.18 mm | 12.7 mm |
Schedule 40 vs Schedule 80 Pipes
Schedule 40: Lighter, cheaper, easier to install, suitable for most residential and commercial applications.
Schedule 80: Thicker walls, stronger, can handle higher pressures, used in chemical plants, oil refineries, and industrial systems.
If you’re just working on a home water line, SCH 40 is usually enough. But if you’re running a high-pressure steam or chemical line, SCH 80 or higher is recommended.
Applications of Different Pipe Schedules
Residential Plumbing: Mostly Schedule 40 for water supply and drainage.
Irrigation Systems: Schedule 40 PVC pipes are common.
Industrial Piping: Schedule 80 and above for pressure lines, chemicals, and gases.
Oil & Gas Pipelines: Schedule 160 or XXS for extreme pressure conditions.
HVAC Systems: Mix of SCH 40 and SCH 80 depending on design requirements.
Tips for Choosing the Right Pipe Schedule
Check the pressure rating of your system.
Consider the type of fluid (water, oil, chemicals, gas).
Ensure material compatibility (steel, stainless steel, PVC).
Factor in cost vs safety—thicker schedules cost more but last longer.
Always consult a pipe schedule chart before purchase.
Final Thoughts
The pipe schedule chart is a vital tool in plumbing, mechanical, and industrial engineering. It helps professionals and DIY enthusiasts choose the correct pipe thickness for safety, durability, and efficiency. Whether you’re working on a household water line or an industrial pipeline, understanding pipe schedules ensures your system performs without leaks or failures.
By using the charts above, you can confidently select the right pipe for your project—balancing strength, flow capacity, and cost.
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