Does ISO 6708 define pipe outside diameters?

No. ISO 6708 defines the DN alphanumeric designation and a preferred series of DN values; DN is dimensionless and does not specify outside diameter, inside diameter, wall thickness or an NPS conversion.

Is NPS the pipe outside diameter in inches?

Not generally. NPS is a nominal designation. For example, NPS 2 has a source outside diameter of 2.375 inches, while NPS 14 and larger in this worksheet have matching numerical OD values.

Why are two metric OD values shown?

The public table value follows the displayed metric cross-reference, while the exact mathematical value is source OD in inches multiplied by exactly 25.4 millimetres per inch. Published metric tables may round differently.

Can this worksheet determine wall thickness or inside diameter?

No. Schedule, material standard and product specification are required. This worksheet intentionally does not calculate wall thickness, inside diameter, pressure rating, tolerance or fitness for service.

Engineering reference worksheet

DN / NPS / OD Cross-Reference

Look up a publicly corroborated DN–NPS pairing and pipe outside diameter. DN, NPS and measured diameter are kept separate.

ISO 6708:1995 — DN only Public table corroboration NPS 1/8 – 24

結果

Source OD

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DN（公称直径）

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NPS（公称パイプサイズ）

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Public table OD

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Exact conversion

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DN	NPS	Source OD (in)	Public table OD (mm)	Exact OD × 25.4 (mm)

What ISO 6708 does—and does not—define

ISO 6708:1995 defines DN as an alphanumeric designation for reference purposes. It consists of the letters DN followed by a dimensionless whole number indirectly related to physical size. The standard supplies a preferred DN series; it does not itself define NPS, outside diameter, inside diameter or wall thickness.

What this worksheet reports

Each row contains four distinct data items: a DN designation, an NPS designation, a source outside diameter in inches, and a publicly displayed metric OD. The calculated value uses only the exact unit identity:

exact OD (mm) = source OD (in) × 25.4 mm/in

Because published tables round metric displays, the public metric value can differ slightly from the exact conversion. For example, 10.750 in × 25.4 = 273.05 mm, while the public table display is commonly 273.0 mm.

Corrected size: NPS 5 has a source OD of 5.563 in and public metric OD of 141.3 mm. A separate 5.500 in / DN125 product size also appears in current manufacturer literature; it must not be substituted for NPS 5.

Scope and limitations

This is an exact-match cross-reference, not a dimensional design calculator. It does not infer a nearest size and does not provide schedule, wall thickness, inside diameter, tolerance, mass, pressure rating, material compatibility or fitness for service. Those require the applicable product/material standard and project specification.

Source limitation: ISO 6708:1995 is verified for the meaning and preferred series of DN. The DN/NPS/OD rows are corroborated against current publicly available manufacturer tables. Direct row-by-row verification against licensed ASME B36.10-2022 Table 2-1 and separate applicability checks for ASME B36.19-2022 remain NEEDS_LICENSED_SOURCE.