NPS / DN / OD Cross Reference — Companion Article

What this tool does

The page looks up pipe size records by NPS, by DN, or by outside diameter. Each result row shows the catalogue, the nominal size, the stored outside diameter, any schedules and standards the catalogue lists, and the equivalent size that shares the same outside diameter.

The records come from PipingDesigners pipe catalogues. The page shows what each catalogue stores. It does not keep its own NPS-to-DN table.

Opening /tools-training/nps-dn-od-cross-reference/ shows the lookup form with no result until you choose a size.

When to use it

Use it when a line list, a vendor drawing, or a specification gives a size in one system and you need the outside diameter, or the matching size in the other system. A DIN line at DN 50 and an ASME line at NPS 2 is the usual case.

Use the outside-diameter lookup when you have a measured or quoted OD and do not know the nominal size. Use it as well for tubing, because OD tubing is not listed as NPS or DN.

Use Pipe by schedule when you need the wall thickness, the bore, or the weight. This page does not show wall thickness.

Inputs

1. Lookup: NPS, DN, or Outside diameter.
2. Units: Metric or Imperial. The page opens on Metric. The browser remembers the choice. Metric leads with millimetres and Imperial leads with inches. The other unit stays on the same line.
3. Nominal size, for an NPS or DN lookup. The list holds the nominal sizes stored in the eligible catalogues for that system.
4. Outside diameter and its unit, in or mm, for an outside-diameter lookup.
5. Look up runs the search.

How it works

An NPS lookup lists every eligible catalogue record stored under that NPS. A DN lookup lists the metric records stored under that DN. An outside-diameter lookup lists every record whose stored outside diameter agrees with the value you typed.

Each record keeps the unit its catalogue stored. A millimetre outside diameter is labelled stored. An inch outside diameter is multiplied by 25.4 to give millimetres, and that figure is labelled converted. The same rule runs the other way when you display inches.

The nominal size is a designation. It is never multiplied by 25.4. NPS 2 is not 50.8 mm, and DN 50 is not 50 mm.

Equivalent sizes are matched on outside diameter. Another size is listed when its OD is within 0.35 mm of the record on the row, after any inch OD is converted at 25.4 mm per inch. The 0.35 mm window is a display comparison. It is not a standard tolerance.

The catalogues searched are AME Ductile Iron Pipes, AME Plastic Pipes, AME Steel Pipes, ASME Pipes and Fittings Catalog, AWWA Pipes and Fittings Catalog, CustomParts Imperial Catalog, DIN Pipes and Fittings Catalog, and ASME BPE STD 2009 Pipes and Fittings. Supplier pipe catalogues are not included.

Understanding the result

The heading repeats the lookup, for example Lookup: DN 50. The table has six columns: Catalogue, Nominal, Outside diameter, Schedules, Standard, and Equivalent size (same OD). An outside-diameter lookup drops the Equivalent column.

Schedules and Standard show what the catalogue lists for that record. Not stated means the catalogue does not list one. Wall thickness is not shown.

No equivalent means no record in the other system has an OD within 0.35 mm. It does not mean the size has no counterpart in practice.

Under the table, an NPS lookup shows an Equivalent DN block and a DN lookup shows an Equivalent NPS block. Each lists the matched sizes and their outside diameters. When no size is close enough the block says: No DN outside diameter is within 0.35 mm of this selection. When another nominal in the same system stores a close outside diameter, the page names it in a separate line.

OD tubing is labelled Tube OD. It is left out of the NPS and DN lists. Use the outside-diameter lookup to find it.

Engineering considerations

An equivalent here is an outside-diameter match. It is not a statement that two pipes are interchangeable. Wall thickness, material, end preparation, and the flange or fitting standard can still differ.

DN 50 and NPS 2 match because 60.3 mm and 60.325 mm differ by 0.025 mm. Two sizes with similar names can be well outside the window. NPS 2-1/2 in the ASME catalogue is 73.025 mm. DN 65 in the DIN catalogue is 76.1 mm. They differ by 3.075 mm, so the page does not pair them.

Some catalogues store more than one outside diameter under the same nominal size. ASME BPE, plastic, and ductile iron records are not the steel pipe outside diameter. Check the catalogue column before using a figure. A DN 65 lookup lists NPS 3 as an equivalent through an ASME BPE NPS 3 record stored at 3.0 in, 76.2 mm. ASME steel pipe NPS 3 is 88.9 mm and matches DN 80.

A converted figure carries the rounding of the catalogue inch value. 2.38 in converts to 60.452 mm, which is not the 60.325 mm of 2.375 in.

Example

DN lookup, DN 50, Metric. One DN record is listed:

• Catalogue: DIN Pipes and Fittings Catalog.
• Nominal: DN 50.
• Outside diameter: 60.3 mm, stored (2.374 in, converted).
• Standard: DIN 2441, DIN 2448, DIN 2458, DIN 2462, EN ISO 1127.
• Equivalent size (same OD): NPS 2.

The Equivalent NPS block reads NPS 2, OD 60.325 mm, converted (2.375 in); 60.452 mm, converted (2.38 in). Both are within 0.35 mm of 60.3 mm.

NPS lookup, NPS 2. The ASME Pipes and Fittings Catalog row is 60.325 mm, converted (2.375 in). It lists schedules 5S, 10, 10S, 30, 40, 40S, 80, 80S, and 160, and standards ASME B36.10, ASME B36.19, ASTM A53, ASTM A106, and ASTM A312. Its equivalent is DN 50. The same lookup also lists AME, CustomParts, and ASME BPE records. ASME BPE stores NPS 2 records at 50.8 mm, 60.452 mm, and 62.992 mm. Only the 60.452 mm record matches DN 50. The Equivalent DN block reads DN 50, OD 60.3 mm, stored.

NPS lookup, NPS 2-1/2. The ASME Pipes and Fittings Catalog row is 73.025 mm, converted (2.875 in), with No equivalent. The Equivalent DN block reads: No DN outside diameter is within 0.35 mm of this selection.

Outside-diameter lookup, 60.3 mm. The page lists the NPS 2 records at 60.325 mm and the DIN DN 50 record at 60.3 mm.

These results were read from the live page on 8 October 2026. The catalogues can grow, so a later lookup may list more rows.

Standards/references (licensed vs interim)

The figures are catalogue values. The disclaimer on the page reads: Catalogue values are evidence from the source catalogue. They are not a code-approved size-conversion table.

The Standard column repeats the standard numbers the catalogue names, such as ASME B36.10, ASME B36.19, and DIN 2448. A citation of a standard number is not a copy of the standard. This page does not reproduce an ASME or ISO size table.

For the interim ASME B36.10 and B36.19 pipe tables, with wall and weight, use Pipe by schedule. Those tables are interim data from public sources, pending the licensed standard.

Limitations/disclaimer

The page is a lookup of catalogue records. It does not certify that two sizes are interchangeable and it does not replace the governing standard.

• Equivalent sizes are an outside-diameter match within 0.35 mm. That window is a display rule, not a tolerance.
• No NPS-to-DN pairing is stored. A pair appears only through matching outside diameters.
• Wall thickness is not shown.
• Supplier pipe catalogues are not included.
• OD tubing is labelled Tube OD and appears only in the outside-diameter lookup.
• Some catalogues store more than one outside diameter for one nominal size. Read the catalogue column.
• Results depend on the catalogue records on the day. Check the result on the page before relying on it.

Use the tool

Calculate now: NPS / DN / OD cross-reference

Related tools

• Pipe by schedule for the interim ASME B36.10 and B36.19 outside diameter, wall, bore, and weight at an NPS. Read the pipe by schedule companion article.
• Flange datasheet for the flange envelope at an NPS and class. Read the flange datasheet companion article.
• Pipe properties for section properties of a pipe.
• Unit converter for a factor between units. Read the unit converter companion article.

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