The Ultimate Guide to Pipe Sizes and Pipe Scheduling [Including Pipe Size Charts]

Understanding pipe sizes and pipe scheduling is essential to the long-term performance of your piping system. Knowing what pipe schedule number you need doesn’t just save you time and money during the shopping process; it can affect everything from load bearing capacity to your piping system’s structure to your ability to identify the right pipe supports and avoid pipe failures. Here is what you need to know about pipe scheduling and pipe sizes.

Jump to Pipe Size Charts →

Why Is Pipe Scheduling Important?

Identifying your pipe’s schedule is important because a pipe’s thickness plays a critical role in your piping system’s longevity. If your pipes are handling a heavier load than they’re prepared to carry, they could snap, burst, leak, or cause additional damage to your piping system. These standard measurements also make it easier to pair your piping with the right pipe supports to enhance your system. If you don’t match your pipes to the right pipe support at the right size, mismatches can cause damage, lead to on-site disasters, and shut down projects.

When Did Pipe Scheduling Start?

Pipe schedules and nominal pipe size (NPS) descended from the Iron Pipe Size (IPS) System. This sizing method established numbers to identify the approximate measurements of pipes. In the early days of the IPS, pipe manufacturers created piping with a fairly consistent thickness.

Yet, as pipe use expanded and piping needed to withstand higher pressures, manufacturers started producing pipes with thicker inner walls. To describe the early discrepancies in thickness, manufacturers classified pipes with three main pipe sizes:

• Standard weight
• Extra-strong
• Double extra-strong

Eventually, as mass production started churning out more and more piping options, there was a need to account for different industries, various piping conditions, and changing pipe temperatures. As a result, in the late 1920s, the American Standards Association created pipe schedule numbers to break pipe wall thickness measurements into smaller increments.

Jump to Pipe Size Charts →

How Do Pipe Sizes Work Today?

Today, there are two pipe classifications that you can use to quickly identify your pipe’s sizing:

1. Nominal Pipe Size
2. Pipe Schedule

These pipe standards help you estimate the full size of your pipe, so you can safely install piping systems, pipe supports, and pipe layouts.

What Is a Pipe Schedule Number?

Pipe schedule numbers are assigned by the American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) to give you a standard set of pipe measurements. They indicate the nominal wall thickness of a pipe. Some of the most common pipe schedule numbers are Schedule 40 and Schedule 80.

What Is Nominal Pipe Size?

In North America, nominal pipe size (NPS) is the standard for identifying pipe sizes. Outside of North America, pipes are identified by nominal diameter, which approximately equates to the outer diameter (OD) of the pipe in millimeters.

Note that an NPS below 14 approximately refers to the diameter of a pipe measured from the center of the wall material to the opposing side center of the wall material, whereas an NPS of 14 or greater matches the outside diameter of the pipe precisely.

Jump to Pipe Size Charts →

What Is Pipe Scheduling?

NPS defines the outer diameter of a pipe, but you also need to determine other factors—such as pipe wall thickness and inner diameter (ID)—to understand a pipe’s full size. This is where pipe scheduling comes in handy.

Pipe schedule is an ANSI/ASME standard that describes a pipe’s nominal wall thickness. The pipe’s schedule number relies on three important things:

• Nominal pipe size
• Your pipe’s working internal pressure
• Your pipe wall’s material makeup

The most prevalent schedule sizes are Schedule 40 and Schedule 80. However, a piping project may stipulate higher schedule numbers.

Why Do We Have Nominal Pipe Sizing?

When we use a “nominal” size, it suggests the number is acting as a representative or approximate measurement, rather than an exact measurement. You may be wondering, “Why do we have nominal pipe sizing at all?”

It’s because pipes can vary dramatically in weight, material, and shape. That means the actual internal dimensions of a pipe can vary among pipes that share the same outside diameter. Nominal measurements assign a number to a pipe’s inner diameter in approximate terms.

What Is Nominal Bore?

Chances are, you’ve also heard the term nominal bore (NB) to describe pipe measurements. But what is nominal bore? It’s simply another name for nominal pipe size. The term is commonly used in countries that operate outside North American and refers to the “bore” or hollow section of a pipe.

What Is Diameter Nominal (DN) Pipe Size?

Diameter nominal (DN) is another pipe sizing term that is often confused with nominal pipe size and nominal bore. Diameter nominal also describes the inside diameter of pipes, but it operates within the metric system, so your pipe’s DN will reflect millimeters instead of inches. For instance, if you have an NPS 2 pipe with a 2” nominal bore, its metric equivalence will be DN 50.

Jump to Pipe Size Charts →

How to Find Your Pipe’s Measurements

You don’t have to scramble and search the internet for every measurement chart available. We’ve put together some fast reference tools to help you identify your pipe’s size, protect your piping system, and launch your next project. Use APP's pipe size charts below to quickly reference key measurements for:

• Pipe Dimensions
• Wall Thickness
• Schedule 40
• Schedule 80
• Type K Copper Tubing
• Type L Copper Tubing
• Type M Copper Tubing

Use APP's pipe size charts below to quickly reference key measurements for:

• Pipe Dimensions
• Pipe Diameter and Wall Thickness
• Copper Nickel Size Chart

Not seeing the size you’re looking for? Have your project made to order.