What is the difference is in Stainless Steel "Pipe" and "Tube"?

Oct 20th 2017

Stainless Steel "Pipe" and "Tube"

We get many questions daily about the size of "pipe" as compared to "tube", for anyone not familiar with the differences this can become very confusing. Many people refer to all round, hollow metals as "pipe", when in fact "pipe" and "tube" are two completely different products and as industry standards go, the fittings and sizes are completely different.

Here is a brief explanation of the two.


Pipe was originally produced to carry liquids inside the pipe and was therefore sized according to the interior capacity. This standard allowed engineers to calculate the amount of volume the pipe could transfer when designing projects.

As such, listed pipe sizes are identified by "Nominal Pipe Size (NPS)" and are generally closer to the inside diameter (ID) of the pipe and have little or no resemblance to the outside diameter (OD).

The wall thickness (W) of the pipe is listed as a "schedule". The larger the number of the " Schedule" the thicker the pipe wall is. However as the pipe size increases, so does the thickness of each schedule. As such, a Schedule 40 pipe in 1 inch NPS, has a thinner all than a Schedule 40 pipe in 3 inch NPS.

Nominal Pipe Size (NPS)
Actual Outside Diameter

1/4 inch
0.540 inch

3/8 inch
0.675 inch

1/2 inch
0.840 inch

3/4 inch
1.050 inch

1 inch
1.315 inch

1-1/4 inch
1.660 inch

1-1/2 inch
1.900 inch

2 inch
2.375 inch

2-1/2 inch
2.875 inch

3 inch
3.500 inch

3-1/2 inch
4.000 inch

4 inch
4.500 inch

5 inch
5.563 inch

6 inch
6.625 inch

8 inch
8.625 inch


Tubing sizes are listed as "Outside Diameter (OD) and Wall Thickness (W). Listed sizes of tubes are exact, a 1 inch "tube" will measure 1 inch on the OD. The "Inside Diameter" (ID) will become smaller as the wall thickness increases.

To find the "Inside Diameter" (ID) of any tube, simply subtract the wall thickness(x2) from the "Outside Diameter" (OD) of the tube.