Trust
Sources and standards
Every number on this site comes from one version-controlled dataset — and every dataset row carries a status: verified, widely published, or approximate. This page lists the references, what each one actually establishes, and what was deliberately not shipped.
References used
ISO 8653:2016 — international ring size standard (EU sizes)
Status: Verified definition; table cross-checked
ISO 8653 defines a ring size as its inner circumference in millimetres. That definition is used in France, Belgium, Austria and the Nordic countries, among others, and is not disputed across any source found. The standard itself is a paid document and is not quoted directly; its 44–72 table was cross-checked row by row using diameter = circumference ÷ π. On this site, the EU column is therefore definitional: EU size = rounded inner circumference in millimetres.
US / Canada ladder — widely published retailer ladder
Status: Widely published, not a quoted standard document
The US ladder on this site (US 3 = 14.07 mm diameter, US 7 = 17.32 mm, US 13.5 = 22.61 mm, in half steps) matches the widely published Primestyle US chart to within 0.03 mm per row. No freely available US standard document was found to cite directly, and this page does not pretend otherwise. US sizes on this site are a lookup table, never a formula.
UK letter system — retailer-published, conflicting
Status: Approximate
UK letters (A–Z, with half letters) come from retailer guides — Beaverbrooks and Queensmith — which disagree in places: a 51.9 mm ring is L on one chart, L½ on another, and between L and M on a third. British Standard BS 8721 is cited by UK retailers for the letter scale, but its full text is not freely available, so it is not quoted here as a verified source. UK sizes on this site are therefore labelled approximate on every page and in every table.
Australia letter system — retailer-published
Status: Approximate
The Australian ladder comes from Joseph George (Australia), whose own guide warns that Australian suppliers differ by up to about 0.3 mm for the same letter. Australian sizes on this site are therefore the same letters as the UK ladder, offset by about 0.3 mm, and labelled approximate.
India numeric system — approximation rule
Status: Approximate
Indian sizes on this site follow the widely published rule: India size ≈ circumference in millimetres minus 40 (so a 54.4 mm ring is India 14). Publishers disagree by about ±1 size around this rule, so India sizes are labelled approximate and the rule itself is stated wherever India sizes appear.
Geometry — bank-card calibration
Status: Definitional (ISO/IEC 7810 ID-1)
The screen sizer calibrates against a standard bank card, 85.60 × 53.98 mm (ISO/IEC 7810 ID-1 credit-card size). That dimension is a published card standard, not a measurement the site invented. If your card is not a standard-size card, calibration against it is invalid and the sizer refuses to guess.
Deliberately not shipped
Japan, Switzerland, Brazil, China and Russia do not have pages or columns on this site. No consistently corroborated ladder was found for those systems, and inventing one would be worse than omitting it. The international chart page explains each omission rather than hiding it. Likewise, no per-size programmatic pages, no brand conversions, and no smart-ring conversions are published — each would require a verified source that does not currently exist for this site.
How to check a number yourself
Every size on this site can be checked with two operations: circumference = π × diameter, and diameter = circumference ÷ π, against the dataset rows in the chart. If a row on this site does not satisfy those relations (within the stated rounding — diameter to two decimals, circumference to one), it is an error, and the editorial policy explains how errors are handled. The full internal source report, including unresolved differences, is kept in the site's documentation as docs/SIZE_SOURCES.md.