Standards and authority

None of the sources read here defines a conversion between national ring sizes

A conversion chart makes a claim about two numbering systems at once. This note asks which document carries that claim, and reports what the primary sources read on 19 August 2026 do and do not contain.

August 19, 2026

The question is which document carries the claim

Suppose you have two conversion charts open and they give different answers for the same finger. Choosing between them by appearance is not possible, because the appearance of a chart says nothing about where its rows came from. The question that can be answered is narrower: which published document does either chart cite, and does that document state the correspondence the row asserts?

This note reports what the primary readings contain: two standards that designate a ring size as a length, and a government circular published in the United States in 1921, which also records the earliest known patent behind the numbering then in use there. None of the sources read states a correspondence between one country's ring numbering and another's.

That is a statement about the sources read on 19 August 2026, and it is deliberately limited to them. It is not a statement that no such document exists anywhere, and it is not a statement about what any national standard says today.

What the two standards designate

ISO 8653:2016 gives ring-size as the circumference of the bigger cylinder that could be inserted in the ring. The quantity designated is a length in millimetres, and what that length means for a single ring is treated on the page that covers the definition rather than here.

The Japanese national standard was made from the same text. JIS S 4700:1998 states that it was produced by translating ISO 8653, first published in 1986, without changing the technical content or the form of the standard, and it defines the size of a ring as the numerical value of the ring's inner circumference expressed in millimetres.

So two of the sources read agree on the quantity, and both express it in millimetres. What follows from that is a limit rather than a chart: a document that designates a length has designated a length, and a correspondence to a foreign numbering is a separate claim that would need its own text. No such text was among the sources read for this page.

The United States record, dated 1921

Every statement in this block belongs to a Bureau of Standards circular published in the United States in 1921, and describes what that document reported at that time.

What the circular set out to find: It examined the cone-type ring gages then in use in the United States, designated by two trade names, and looked for the dimensions their numbers corresponded to.
No printed dimensional definition was found: The circular reports finding no printed document that established which dimensions the numbers on those gages stood for.
One standard in appearance, several in practice: It states that while there apparently was only one standard in use in the United States, in reality there were several similar ones, and attributes this to the absence of specific dimensions and to errors introduced by adopting a common commercial sample as the pattern.
The same number, different diameters: Letters from two manufacturers gave the diameter for size 1 as 0.485 inch and as 0.491 inch. Across the retail gages examined, size 1 fell between 0.480 and 0.491 inch, and size 13 between 0.870 and 0.878 inch.
The numbering predates any definition found for it: The conical gage numbered 1 to 13, with quarter sizes, was in use at least from 1874, and the earliest known patent for it, granted to F. E. Allen on 3 February 1874 as US Patent 146974, described the gage without stating dimensions.

What this leaves you holding

If a size arrives as a length in millimetres, it corresponds to a published definition, and it can be compared with a measurement of an actual ring. If it arrives as a national number, the sources read here do not say what length it stands for, and this note does not supply one.

That is a smaller answer than a chart, and it is a different kind of answer. A chart offers a value; a record of what was read offers a boundary. Within that boundary the practical move is to carry the number in the form it was given, together with the system it belongs to and the party who supplied it.

Nothing here is an instruction about which size to make or sell. It is a report of what four documents contain, read on one date.

Boundaries of this note

No conversion between US, UK, EU and Japanese numbers is published, reconstructed or approximated here, in any direction.
No step value is given: nothing here states what one whole size is worth in millimetres or in fractions of an inch.
No claim is made about what a national standard in any country states today. The United States evidence used here is dated 1921.
The official definition of the United Kingdom letter sizes is not represented, because the British standard text could not be obtained for this reading.
What a ring size number designates for a single ring belongs to the page on the definition, and is used here only as far as the argument requires.
Why two measurements of one ring can differ belongs to the page on measuring method, and is not addressed here.
Nothing on this page describes an application converting, validating or recommending a ring size.
All statements belong to the reading made on 19 August 2026.

Questions

Is there an official conversion between US, UK, EU and Japanese ring sizes?

None of the sources read for this page defines one. ISO 8653:2016 and JIS S 4700:1998 designate a size as the inner circumference in millimetres, and the United States material read is a 1921 Bureau of Standards circular reporting that no printed dimensional definition was found for the numbers then in use there. This page publishes no conversion of its own.

Does that mean the United States has no ring size standard today?

This page cannot say. The United States evidence read here is dated 1921 and describes the situation the circular found at that time. Whether a national standard was established there afterwards was not read for this page, so no claim is made either way.

Where do the letter sizes used in the United Kingdom come from?

The British standard text, BS 6820 and BS EN 28653, could not be obtained for this reading, so its definition is not represented here. Nothing about the letter system is inferred from the other sources.

If the standards state a size in millimetres, why does my supplier use a number?

The documents read here designate the standard's quantity; they were not read as accounting for other numbering in commercial use. What a supplier's number refers to has to come from the supplier's own specification, not from this page.