Enter a size in the system you know and get its equivalent in twelve countries, plus the exact circumference and diameter. Every scale is verified at jewellers in the country concerned, not copied from an international chart.
In France, Germany, Switzerland, Austria, the Netherlands and across almost all of Europe, the size IS the finger circumference in millimetres. A 52 measures 52 mm.
Finger circumference
52,0 mm
The inner circumference, which everything else derives from.
Inner diameter
16,55 mm
What a rule laid across the ring measures.
The same ring, in the other systems
A size is a measurement, not a fixed value: the same finger varies by about one size over the course of a day, with heat and exertion. For a purchase that matters, measure twice, at two different moments.
Compare three online size converters and you will often get three answers half a size apart. That is not inevitable. It is a question of method.
Every sizing system reduces to a single physical quantity: the inner circumference of the ring, in millimetres. Everything else is a national convention laid over it. An accurate converter applies the definitions; a copied one inherits its source's rounding, and stacks more on top.
The "French size" printed in international charts does not exist.
Many international charts present a system where the size equals the circumference minus 40, a 12 for 52 mm, and label it "French". No French jeweller uses that notation. In France the size is the finger circumference in millimetres: 52, 53, 54, in line with ISO 8653. That minus-40 system is real, and in fact widespread: Italy, Spain, Brazil, Turkey and mainland China all use it, each publishing it at its own jewellers. It simply is not French.
Germany counts in circumference, but its older notation still circulates.
Germany and the Netherlands count in circumference today, exactly as France does: German retailers state plainly that the size is the inner circumference, and a ring 18 mm across is sold there as a size 57. But the older diameter convention still circulates on documents and sizers, where a “size 17” means 17 mm of diameter, that is 53.4 mm around the finger. The two ranges never overlap, so the order of magnitude is enough to tell them apart, and this converter flags it rather than calculating into thin air.
Two systems that give the same number, right up until 57 mm.
Up to about 57 mm, the Japanese size and the Italian size are almost the same number: a 48 mm ring is an 8 in both, a 52 mm ring a 12, a 55 mm ring a 15. Hence the charts that merge the two columns. They are nevertheless two different systems, and they part company higher up: at 60 mm Italy says 20 and Japan says 19. The Japanese scale is defined on the diameter in steps of a third of a millimetre, the Italian one on the circumference in steps of a millimetre. They could only ever coincide by accident, and the accident runs out.
Two reliable methods, and the mistakes that skew the result.
On national systems, measuring, and its limits.
In France, a woman's ring finger most often falls between 50 and 54, a man's between 60 and 62. These are orders of magnitude only: hands vary far more than the averages suggest, and a ring meant as a gift is always better chosen from a measurement than from a statistic.
Because they confuse the French system with the Italian one, where the size equals the circumference minus 40. In France the size is the finger circumference in millimetres: a 52 mm ring is called size 52, never size 12. In Italy that same ring genuinely is a size 12. The error is widespread in international conversion charts.
A diameter, that is 53.4 millimetres around the finger. Germany does count in circumference today, exactly as France does: major German retailers sell a ring 18 millimetres across as a size 57. The older diameter notation still circulates, but the two ranges never overlap: the diameter of a worn ring falls between 15 and 22 millimetres, a circumference between 47 and 69.
Usually yes, by around two sizes in each direction, but it depends entirely on the design. A plain band is easy to alter; a full eternity ring, a continuous pattern, or a piece in titanium or ceramic cannot be resized, or only poorly. Ask before you buy.
They are calculated from each system's official definition, always going through the inner circumference, rather than copied from an existing chart. Each formula is checked against values published by sources in the country concerned, and those checks are documented in the tool's source. That is why small differences appear against other converters, many of which inherit successive roundings.
In Liink the size travels with the order, from the request through to the workshop sheet. Your manufacturers see the size you ordered, with no re-entry and no rough conversion.
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