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Pipe Schedule Chart Explained

Pipe schedule numbers (SCH) are one of the most confusing concepts for new engineers and buyers. This guide breaks down what schedule numbers actually mean, how wall thickness varies by pipe size, and when to use each schedule.

Updated: September 15, 2026·8 min read

What Does Pipe Schedule Mean?

A pipe schedule (SCH) is a standardized wall thickness designation used in the pipe industry. The schedule number tells you how thick the pipe wall is relative to its nominal pipe size (NPS). Higher schedule numbers mean thicker walls and higher pressure ratings.

The schedule number system was developed by the American National Standards Institute (ANSI) and is now maintained under ASME B36.10M for carbon and alloy steel pipes, and ASME B36.19M for stainless steel pipes.

Key Insight

Pipe schedule is NOT a direct measurement. A SCH 40 pipe has different wall thickness depending on the pipe size. For example, NPS 1/2" SCH 40 has 2.77 mm wall, while NPS 12" SCH 40 has 10.31 mm wall. The schedule number represents a ratio of pressure capacity, not a fixed dimension.

Pipe Schedule Wall Thickness Chart

The following chart shows wall thickness (in millimeters) for common pipe schedules at various NPS sizes. All dimensions follow ASME B36.10M.

Schedule	NPS 1/2"	NPS 2"	NPS 4"	NPS 8"	NPS 12"
SCH 5	1.24	-	-	-	-
SCH 10	2.77	2.87	3.38	-	-
SCH 20	3.38	3.91	-	-	-
SCH 30	4.55	5.56	-	-	-
SCH 40	6.02	7.11	8.18	9.27	12.70
SCH 60	7.62	10.97	12.70	-	-
SCH 80	11.13	15.09	18.26	21.44	25.40
SCH 100	14.02	19.05	-	-	-
SCH 120	17.12	23.83	28.58	-	-
SCH 140	21.41	29.36	33.32	-	-
SCH 160	26.97	36.53	40.49	46.02	50.01
STD	6.35	7.14	8.74	10.31	12.70
XS	8.74	11.13	13.49	15.88	19.05
XXS	15.88	22.23	28.58	34.93	50.01

Wall thickness in millimeters. "-" indicates the schedule is not commonly available at that size.

Common Pipe Schedules and Their Uses

SCH 40 (Standard Weight)

The most common pipe schedule for general-purpose applications. Used for water, air, oil, and gas lines at moderate pressures. Available in NPS 1/8" through NPS 36" and larger. For NPS 10" and below, SCH 40 is the same as "Standard" (STD).

SCH 80 (Extra Strong)

Thicker wall for higher-pressure applications. Common in chemical processing, high-pressure steam, and hydraulic systems. For NPS 8" and below, SCH 80 is the same as "Extra Strong" (XS).

SCH 160 & Double Extra Strong (XXS)

Heavy-wall pipe for very high-pressure or high-temperature services. SCH 160 is available up to NPS 24". XXS has even thicker walls and is typically available up to NPS 12". These are used in power plants, refinery high-pressure lines, and severe service applications.

SCH 5 & SCH 10 (Light Wall)

Thin-wall pipe used for low-pressure applications where weight and cost matter. Common in HVAC, fire sprinkler systems, and stainless steel process lines. SCH 10 is especially popular for stainless steel piping because it offers good flow capacity with reduced material cost.

How to Read a Pipe Schedule Chart

To find the correct pipe wall thickness, you need two pieces of information:

Nominal Pipe Size (NPS) — The approximate inside diameter in inches (e.g., NPS 2", NPS 4")
Schedule Number (SCH) — The wall thickness designation (e.g., SCH 40, SCH 80)

With these two values, you can look up the exact wall thickness, outside diameter, and inside diameter from the ASME B36.10M table. Remember that NPS is NOT the actual inside diameter — it is a trade name. The actual dimensions depend on the schedule.

Example: NPS 4" SCH 80

Outside Diameter: 114.3 mm (4.500")
Wall Thickness: 8.56 mm (0.337")
Inside Diameter: 97.18 mm (3.826")
Weight per meter: ~22.3 kg (carbon steel)

Pipe Schedule vs Pressure Rating

Pipe schedule is related to pressure capacity, but the relationship is not linear. The same schedule number can handle different pressures depending on the pipe material and temperature. For example:

NPS 2" SCH 40 carbon steel: ~2,000 psi at ambient temperature
NPS 12" SCH 40 carbon steel: ~1,400 psi at ambient temperature

Always check the actual pressure-temperature rating for your specific pipe material and size. The schedule chart gives you dimensions, not pressure ratings.

Frequently Asked Questions

What is the difference between SCH 40 and SCH 80?▼

SCH 80 has a thicker wall than SCH 40 for the same pipe size. This means higher pressure capacity but also higher weight and cost. For example, NPS 2" SCH 40 has 3.91 mm wall, while SCH 80 has 5.54 mm wall.

Is schedule the same as pressure class?▼

No. Pipe schedule refers to wall thickness, while pressure class (e.g., Class 150, 300, 600) is used for flanges and fittings. They are related but different systems. A SCH 80 pipe may be paired with a Class 300 flange, for example.

What does STD, XS, and XXS mean?▼

STD = Standard (same as SCH 40 for NPS 10" and below), XS = Extra Strong (same as SCH 80 for NPS 8" and below), XXS = Double Extra Strong. These are older designations that predate the schedule number system but are still widely used.

Can I use the same schedule for stainless steel?▼

Stainless steel pipes follow ASME B36.19M, which uses the same schedule designations but limits the available schedules to SCH 5S, 10S, 40S, and 80S for most sizes. The "S" suffix indicates stainless steel. Wall thicknesses are identical to the corresponding carbon steel schedules.

Calculate Pipe Weight Instantly

Use our free pipe weight calculator with built-in schedule chart data. Select NPS, schedule, and material to get exact weight per meter.

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