Square Tubing Sizes . Rectangular Tubing Sizes Laser Square Stainless Steel Stainless Steel .The following is an overview of how and pipe size is measured and handled. OD and Nominal Pipe Size. Tubing is measured by the OUTSIDE DIAMETER O.D. , specified in inches e.g., . or fraction of an inch eg. . Pipe is usually measured by NOMINAL PIPE SIZE NPS ..Sizes and dimensions of pipes ands, and their fittings inside and outside diameter, weight and more.This stainless steel tubing chart provides a handy reference for extra thin XX and heavy H wall dimensions of hard tempered, and grade stainless steel tubing in standard gauges and half gauges .