Understanding Steel Pipe Sizes



Understanding Steel Pipe Sizes

Pipe SizesOn our website we have included a standard pipe chart that you can use to help you in getting a quote from a pipe distributor. There are many pipe standards and charts for different products, so we thought we would shed some light on the pipe chart you are viewing. 

The first column of the pipe chart is the “Size” which is the “Nominal Pipe Size” (NPS) if you find literature on NPS you will note that it refers to a set of standard pipe sizes used for pressure piping in North America, but it is also used for many other types of steel pipe. Pipe sizes have two non-dimensional numbers: a Nominal Pipe Size (NPS) and a schedule (SCH). The relationship between these numbers and the actual pipe dimensions can be a bit confusing. If you ask for 4 inch sch 40 pipe the actual outside diameter of the pipe is 4.50 inches and not 4 inches. 

To explain how that works, the NPS is very loosely related to the inside diameter in inches, but only for NPS 1/8” to NPS 12”. For sizes of 14” and larger, the NPS is equal to the outside diameter (OD) in inches. For a given NPS, the OD stays constant and the wall thickness increases with larger SCH. For a given SCH, the OD increases with increasing NPS while the wall thickness increases or stays constant. Pipe sizes are documented by a number of different standards. 

The most commonly used schedules today are 40, 80, and 160. Now, sch 40 needs a few moments of our time. There is a misconception that “sch 40” is “standard” but as you can see on the pipe chart they are not the same all the time. For NPS sizes from 12” and larger sch 40 and standard are different wall thicknesses.

The various standards for pipe schedule are not identical. Frequently some sizes or in some cases an entire schedule are present in some standards but not others. When different standards do overlap, they usually have the same dimensions. 

As you can see some specifications use pipe schedules called Standard Wall (STD), Extra Strong (XS), and Double Extra Strong (XXS), although these actually belonged to an older system called iron pipe sizes (IPS). The IPS number is the same as the NPS number. STD is identical to SCH 40S, and 40S is identical to 40 for NPS 1/8 to NPS 10, inclusive. XS is identical to SCH 80S, and 80S is identical to 80 for NPS 1/8 to NPS 8, inclusive. Different definitions exist for XXS, but it is generally thicker than schedule 160.

Now, the content above is our representation of the steel pipe chart and we only mention this to assist you on how we look at new and used steel pipe sizes. Always consult your dealer before purchasing any steel products.

Now that we have shed some light on pipe charts and sizes, browse our construction materials and services directory to find some pipe.