OD vs. ID vs. Nominal Pipe Sizes: Learn the Differences in the Details

There’s a popular saying that goes, “The devil is in the details,” but with regards to pipe sizing, it’s all about the differences in the details. Three of the most widely used measurements for piping are OD or outer diameter, ID or inner diameter, and nominal diameter. In this guide, you will learn:

– The definition of each pipe size

– Differences in dimensions

– Related charting

Why Is Knowing Pipe Sizing Important?

Before getting to know how are pipes measured, you must first realize the importance of sizing. Knowing the right sizing for your pipes is vital to ensure plumbing efficiency and reliability, regarding plumbing, heating, and other fluid systems, avoiding issues, such as water hammer, excessive pressure drops, and expensive repairs, while likewise optimizing system performance and all-around longevity. 

There are five various factors that influence pipe sizing:

• The flow rate, or the amount of fluid that must be moved through the pipe for each time unit. 
• The pipe length, or the distance the fluid needs to be able to travel.
• The fluid type, or the fluid properties, such as density and viscosity, that affect the flow characteristics.
• The fitting and valves themselves, or the components that introduce friction and pressure drops, which must be factored into the sizing calculations, though. 
• The pipe material, or the one that affects the pipe’s resistance to corrosion and pressure.

Sizing Definitions

OD or Outer Diameter

What is outer diameter? Well, the outer diameter or external diameter is the pipe size measured from one outside edge toward the opposite outside edge, duly measuring the maximum width of the pipe’s outside area. 

Its importance? Measuring this size is crucial in closer spaces, which could limit the amount of piping you can place in areas where there’s limited space availability. 

ID or Inside Diameter

On the other hand, ID or inside diameter covers the distance from the pipe’s interior edge to the opposite inside edge, measuring the maximum measurement within the pipe.

Concerning the importance of this measurement, this impacts how much the pipe material can contain at any given time, impacting flow rates. 

Nominal Diameter

This time, nominal diameter is much easier to understand. It also defines the pipe’s size, but this is dimensionless. For instance, the nominal size of four inches schedule 80 pipe is four inches, but the outside diameter is actually 4.5 inches. It is crucial to note the outside diameter does not rely on its thickness. Remember this. This time, let’s head over to the differences in dimensions, to help you better comprehend.

Differences in Dimensions

The definitions can only teach you so much, but an in-depth look at the differences between those pipe sizes are upon their dimensions. Read on. 

External Diameter

So, first, ask yourself, how do you measure a pipe diameter? When you measure the outside of an inch pipe, you will realize it is actually 1.315 inches across. The rationale behind this is simple. It also considers the pipe walls’ thickness. 

Internal Diameter

Meanwhile, when it comes to internal diameter, it is always tinier than the corresponding OD. This is due to the walls of the pipe. For instance, an inch schedule 40 pipe features an outside diameter of 1.315 inches, but its inside diameter shall only be 1.049 inches. 

Nominal Pipe Size

Now, what about for the nominal pipe thickness? This pipe sizing is a standard way of measuring pipes in almost every region of North America. A number is used to describe the pipe sizing, but take note it does not measure the pipe’s width per se. For example, a two-inch NPS value. Here, the external diameter value shall be roughly 2.375 inches.

By now, it will be easier to conclude from the information on the pipe sizing. However, before that, you might want to check out this comprehensive pipe measurement chart to visualize what you’ve read above.

Conclusion

Just like choosing the right size for your formalwear, you must first find the right size for your pipe before you make the purchase. Pipe sizing is only the standard designation, but there’s outside diameter, inside diameter, and nominal pipe size. Accurate measurements ensure the best performance and proper fit in piping systems.

YOUFUMI, our manufacturing brand, features lined pipe fittings in our catalog. With the ideal products of this kind, you can facilitate the installation and the spare parts in your operations. Find out more about our company today.

Reference

The Difference in the Details: OD vs ID vs Nominal Pipe Size (1)

OD vs ID vs Nominal Pipe Size – All Differences Explained (2)

4 Reasons Why Pipe Diameter Is Important (3)