For most common sizes, nominal copper tube size is approximately 1/8 inch less than actual outside diameter: 1/2 inch nominal is 5/8 inch actual, 3/4 inch nominal is 7/8 inch actual, and 1 inch nominal is 1-1/8 inch actual. This is a legacy of how copper water tube was originally standardized, and is a completely different convention from steel or PVC nominal pipe sizing.

While green, blue, and red stripes commonly correspond to Type K, L, and M respectively in the U.S. market, color coding is a common industry convention, not a guaranteed universal identifier. Always confirm with the printed text marking or measured dimensions rather than color alone.

ASTM B306 covers seamless copper drainage tube as a distinct product from ASTM B88 water tube. DWV tube is not rated for pressurized water supply service and should never be substituted into a pressure application.

A 1/2 inch nominal copper tube (0.625 in OD) is smaller than a 1/2 inch nominal steel or PVC pipe (0.840 in OD), because copper tube uses an entirely different nominal sizing convention than the NPS system used for steel and PVC. Never assume fittings, adapters, or dimensions transfer directly between these materials at the same nominal label. See the PVC Pipe Size Chart and Pipe Wall Thickness Chart for the NPS-based systems.

Working (operating) pressure and burst pressure are distinct concepts. Burst pressure represents a failure condition and should never be treated as an acceptable operating value; published copper tube references distinguish drawn and annealed tube burst pressures at room temperature specifically because they differ from safe operating limits.