Sizes, codes and marks

Category · 8 entries · Updated October 29, 2026

Pipe sizes are names, not measurements, and the letters printed along a pipe say which standards it meets. These entries decode sizes, the NSF/ANSI marks for drinking water, lead-free rules and the model plumbing codes that states and cities adopt.

Entries in this category

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  Nominal pipe size, CTS and IPSWhy pipe sizes are names rather than measurements, and how the CTS and IPS outside-diameter systems differ for the same nominal size.
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  Pipe sizing basics for housesHow water supply pipe sizes for a house are chosen: code minimums, flow, velocity and pressure, and why the job belongs to a plumber.
• NSF/ANSI/CAN 61The health-effects standard for products that touch drinking water: what NSF 61 tests, what it covers and where codes require it.
• NSF/ANSI/CAN 372 (lead content)The standard used to certify plumbing products to the federal 0.25% lead-free limit, and how to read its marks.
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  NSF/ANSI 14 (plastics piping)The NSF standard for plastic pipe, fittings and related materials, and what its pw, dwv and other end-use marks mean.
• Plumbing codes: IPC, UPC and IRCThe three main US model plumbing codes, who writes them, what each covers and how states and cities adopt them.
• Lead-free solderSolder and flux with no more than 0.2% lead, the only kind allowed on US drinking-water plumbing since 1986.
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  Reading the print line on pipeWhat the printed or stamped text along PEX, copper and plastic pipe means: size, standards, ratings, listings and date.