Pipe Standards by Country

One Name, 6 Different Diameters

Ask what a DN 65 pipe measures and the honest answer is another question: under which standard? The spread across the families in use is 3.3 mm on the outside diameter, which is far more than the clearance a threaded or welded fitting is built for.

For the full dimension table under the American series, see the pipe size chart. For why the number on the pipe never matched what you measure, see what nominal pipe size means.

The American Series Is the One That Differs

Put every series side by side and the usual framing inverts. It is not that the world scatters around the American figure; it is that the American figure sits apart from a broad consensus, at two sizes in particular. At DN 65 every other series in use says roughly 76 mm and ASME says 73.0. At DN 125 the others say 139.7 to 140 and ASME says 141.3. Everywhere else the agreement is close enough to ignore.

That matters because most English-language pipe charts publish the American series without saying so. A fitter in Manila or Lagos reading one of those charts is being handed the dissenting figure as though it were the settled one — and at DN 65 the gap is 3.3 mm, which is a weld-prep failure rather than a rounding difference.

The disagreement is not uniform across the range, either. Measured as a share of the pipe rather than in millimetres, it is worst at the small end, where most plumbing and service pipe lives, and settles down as the pipe grows. Only one size in the common range is a size the world genuinely agrees on.

Two of these systems do not publish a DN column at all. GOST designates pipe as outside diameter × wall thickness and nothing else; GB/T 17395 is a flat list of permitted outside diameters. The DN values shown for those two families are trade convention rather than standards text, which is exactly the sort of distinction this table exists to keep visible.

What “Verified” Means Here

Of 157 countries, 16 have been checked against the national standard itself. The remaining 141 are inferred from the standards family the country belongs to — a sound working assumption, and not the same thing as a confirmed fact.

Every inferred row below carries a visible label. Saying which of these we could not confirm is the point of the page, not a gap in it. How this data was verified, and what could not be.

A country reaches the verified column only one way: somebody read the dimension table in that country’s own standard and compared it, value by value, with what this site publishes. Agreement between three websites does not count, and on this dataset it repeatedly would have been wrong — five clusters of pages were found reproducing one another’s figures verbatim, so what looked like three independent confirmations was one source counted three times.

The inferred rows are not guesses. A country is placed in a standards family on the basis of the standards body it belongs to and the series its national standard adopts, and for most of the world that inference is sound: an EU member state works to EN, a country in the Gulf co-operation area generally works to the American series through API and ASME. What is missing is confirmation, and the difference between a sound inference and a checked fact is the whole reason this column exists.

How to Use This If You Are Ordering

The practical question is rarely “which standard does my country use” on its own. It is whether the pipe in front of you will mate with the fitting in the box. Three rules follow from the table, and they hold regardless of which row your country sits on.

Order on the outside diameter, not the size name

The name is the ambiguous part. A purchase order that says “DN 65, outside diameter 76.1 mm” cannot be filled with the wrong series; one that says “2½ inch” can, and at that size it differs by 3.3 mm.

Check the size, not the country

Most sizes agree closely enough that the standard on the paperwork makes no practical difference. A few do not. Look up the size you are actually buying rather than assuming the whole range moves together, because it does not.

Imported stock does not follow the local standard

The row for a country describes what its standard specifies, not what its merchants happen to hold. In much of South Asia, Africa and the Caribbean the stock on the shelf was made somewhere else and follows the standard of the country that made it. Where the two disagree, the pipe wins.

Every Country We Have Mapped

Showing 157 of 157 countries

Standards families are compiled from the published national standards listed in the verification method. A country is marked verified only where the national standard itself was checked; 141 of 157 are inferred from the family and labelled above.

Frequently Asked Questions

Does pipe size change from country to country?

The nominal size names are shared, but the diameters behind them are not. A DN 65 pipe measures 73.0 mm across the outside under ASME, 76.1 mm under EN 10220 and 76.3 mm under JIS. Those are three different pipes sold under one name.

Why is the American size the odd one out?

ISO 4200, the international series most national standards descend from, places 76.1 mm in Series 1 — its preferred tier. It places 73.0 mm in Series 3, which the standard describes as sizes for special application, some of which may be withdrawn in due course. ASME kept the Series 3 value.

Which countries are verified on this page?

Sixteen of the 157. A country counts as verified only when the dimensions were checked against the national standard itself. The other 141 are inferred from the standards family the country belongs to, and every one of them is labelled as unverified rather than presented as fact.

What does it mean if my country is marked unverified?

It means the pipe sold there almost certainly follows the standards family shown, but nobody has checked the national standard document itself. The figure is a good working assumption, not a confirmed one, and it should not be used where the exact diameter matters.