Schedule 40 is a standardized wall thickness for pipes, defined by the "American Society of Mechanical Engineers (ASME)" standards. It is the most common and versatile pipe schedule used for a wide range of medium-duty applications involving water, air, gas, and structural uses.
Think of it as the "standard weight" of pipe. It's not a material or a specific size, but a designation of how thick the pipe's wall is.
What does schedule 40 pipe mean?
1. It's About Wall Thickness, Not Diameter
The key to understanding "Schedule" is to know that it defines the wall thickness for a given nominal pipe size (NPS).
Nominal Pipe Size (NPS): This is a loosely based name for the diameter. For example, a "1-inch" NPS pipe does not have a 1-inch inner or outer diameter. It's just a name for that size class.
Schedule (SCH): This number tells you the wall thickness. A higher schedule number means a thicker wall, which makes the pipe stronger and able to handle higher pressure.
- Example:
A 1" NPS pipe always has the same outer diameter (1.315 inches), regardless of its schedule.
Schedule 40 has a wall thickness of 0.133 inches.
Schedule 80 has a wall thickness of 0.179 inches.
Schedule 160 has a wall thickness of 0.250 inches.
As you can see, for the same "1-inch pipe," the wall gets progressively thicker, and the inner diameter (ID) gets smaller.
2.Pressure Rating
The primary reason for the thicker wall is to contain higher internal pressure.
Schedule 40 is suitable for many common, medium-pressure applications like domestic water lines, drain lines, compressed air systems, and low-pressure steam.
Schedule 80 has a higher pressure rating and is used for more demanding industrial applications.
Schedule 5 & 10 have thinner walls and are used for low-pressure applications.
What is the thickness of Schedule 40 pipe?
The thickness of a Schedule 40 pipe depends entirely on its Nominal Pipe Size (NPS).
This is the most critical point to understand: There is no single thickness for Schedule 40. A 1-inch Schedule 40 pipe has a different wall thickness than a 2-inch Schedule 40 pipe.
The Nominal Pipe Size (NPS) is a loosely based name for the diameter. For example, a "1-inch" NPS pipe does not have a 1-inch inner or outer diameter. It's just a name for that size class.
Here is a table with the wall thickness for common sizes of Schedule 40 Carbon Steel Pipe (per ASME B36.10M):
| Schedule 40 Pipes Size Chart | |||
| Nominal Pipe Size (NPS) | Outer Diameter (OD) | Schedule 40 Wall Thickness | Inner Diameter (ID) |
| 1/8" | 0.405 inches | 0.068 inches | 0.269 inches |
| 1/4" | 0.540 inches | 0.088 inches | 0.364 inches |
| 3/8" | 0.675 inches | 0.091 inches | 0.493 inches |
| 1/2" | 0.840 inches | 0.109 inches | 0.622 inches |
| 3/4" | 1.050 inches | 0.113 inches | 0.824 inches |
| 1" | 1.315 inches | 0.133 inches | 1.049 inches |
| 1 1/4" | 1.660 inches | 0.140 inches | 1.380 inches |
| 1 1/2" | 1.900 inches | 0.145 inches | 1.610 inches |
| 2" | 2.375 inches | 0.154 inches | 2.067 inches |
| 2 1/2" | 2.875 inches | 0.203 inches | 2.469 inches |
| 3" | 3.500 inches | 0.216 inches | 3.068 inches |
| 3 1/2" | 4.000 inches | 0.226 inches | 3.548 inches |
| 4" | 4.500 inches | 0.237 inches | 4.026 inches |
| 5" | 5.563 inches | 0.258 inches | 5.047 inches |
| 6" | 6.625 inches | 0.280 inches | 6.065 inches |
| 8" | 8.625 inches | 0.322 inches | 7.981 inches |
| 12" | 12.75 inches | 0.406 inches | 11.938 inches |
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