What Do Pipe Schedules Mean?

The schedule number on pipe products relates to the thickness of the wall on the pipe: as the number increases, the thicker the wall thickness becomes. Also, while the schedule number can be the same on different sized pipes, the actual wall thickness will be different. Here are a few examples of this:

Pipe size 1.000” Schedule 40 – The actual wall thickness is 0.133” or 3.378 mm

Pipe size 1.000” Schedule 80 – The actual wall thickness is 0.179” or 4.547 mm

Pipe size 2.000” Schedule 40 – The actual wall thickness is 0.154” or 3.912 mm

Pipe size 2.000” Schedule 80 – The actual wall thickness is 0.218” or 5.537 mm

What we can see here is that the schedule number increases the wall size, and that the wall thickness changes based on the nominal pipe size (NPS).

There are several schedule numbers used on pipe, such as schedules:  5, 5S, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD, XS and XXS. The most common ones used are schedules 40 and 80

What does Nominal Pipe Size or NPS mean?

In 1927 the American Standard Association replaced the previously used Iron Pipe Sizing (IPS) with Nominal Pipe Sizing (NPS).  This North American standard is used on pipes for high or low pressures and temperatures. The European designation equivalent to NPS is DN (diamètre nominal/nominal diameter/Durchmesser nach Norm), in which sizes are measured in millimetres.

The NPS size represents the approximate inside diameter (not outside) of the pipe; if the schedule number on a set size is changed, it does effect the inside diameter (ID) but not the outside diameter (OD).  Example:

NPS                        OD                          Schedule #          Wall Thickness           ID

1.000”                   1.315”                   SCH 40                  0.133”                         1.049” (approx. 26.644 mm)

1.000”                   1.315”                   SCH 80                  0.179”                         0.957” (approx. 24.307 mm)

All pipes are specified using the NPS and schedule numbers, it is the schedule number that determines the approximate inside diameter.

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