Ring sizes
Every ring-size conversion chart on the web shows US, UK and metric as three equally solid columns. They are not equally solid. ISO 8653:2016 is a current international standard that fixes the size, the instrument, the tolerances and the point on the ring where you take the reading. BS EN 28653:1993 was withdrawn on 25 March 2026. And the United States has never had published dimensions at all— not an inference, but what its own Bureau of Standards put in print in 1921.
This page publishes no conversion table, deliberately.The UK letter-to-millimetre figures sit behind BSI’s paywall, and the freely available versions trace back to trade sites or to a Wikipedia article carrying an “original research” banner. A chart whose provenance stops at another website would be the most-used wrong answer here, because a ring bought a size out is a ring that does not fit. Systems are added to this page when a primary source can be read — which is why there are three.
This page publishes no conversion table, deliberately.The UK letter-to-millimetre figures sit behind BSI’s paywall, and the freely available versions trace back to trade sites or to a Wikipedia article carrying an “original research” banner. A chart whose provenance stops at another website would be the most-used wrong answer here, because a ring bought a size out is a ring that does not fit. Systems are added to this page when a primary source can be read — which is why there are three.
3 entries
All cited
SortedA–Z
| Name | How a size is written | Standard status | Defining body | Where the ring is measured | Stated tolerance |
|---|---|---|---|---|---|
| ISO 8653 (metric) | A number from 41 to 76. ISO defines ring-size as “circumference of the bigger … | Current international standard, second edition, published 15 January 2016. It … | ISO, through technical committee TC 174 (Jewellery). | Defined explicitly, and differently for two profiles. On a ring with a ROUNDED… | Yes. The metric ring stick must have a measurement scale 160,0 mm ± 0,5 mm lon… |
| United Kingdom (letters) | Letters rather than numbers. The technical content — which letter corresponds … | WITHDRAWN. BSI records BS EN 28653:1993, “Jewellery. Ring-sizes. Definition, m… | BSI, as the British adoption of a European adoption of the ISO standard. | — | — |
| United States (numeric) | A number, on gauges graduated 1 to 13 or 0 to 13 with quarter sizes. The Burea… | No published dimensional standard, stated as such by the national standards bo… | None. The Bureau of Standards stated in 1921 that it intended to take the prob… | Not fixed, and the Bureau treated this as a distinct problem in its own right:… | — |
Showing all 3Every figure traces to a named source with a pinpoint locator. Values we could not source are left blank rather than estimated.