European Ring Sizes Explained: ISO, France, Germany and Switzerland
How the ISO circumference standard works and how the French, German and Swiss scales relate to it, with worked conversion examples.
6 min read
Europe looks like it has one sizing system and in fact has four, all derived from the same physical measurement.
The ISO standard
ISO 8653 defines ring size as the inside circumference in millimetres. A size 54 ring measures 54 mm around the inside, which is a 17.2 mm diameter. This is the standard used in Italy, Spain, the Netherlands, Scandinavia and increasingly everywhere else in Europe. It is the cleanest system in the world because the size is the measurement.
France
French sizing takes the ISO circumference and subtracts 40. A French 14 is a 54 mm ring; a French 8 is a 48 mm ring. Some older French charts subtract 39 or use half steps, so confirm with the retailer when the numbers look one size out.
Germany
German sizing quotes the inside diameter in millimetres, usually to one decimal place. A German 17.2 is the same ring as an ISO 54. The confusion arises when a listing prints "17" with no unit; if the surrounding numbers are in the teens it is a diameter, if they are in the fifties it is a circumference.
Switzerland
The Swiss scale runs roughly from 0 to 27 in half steps, approximately the ISO circumference minus 39.5. A Swiss 14.5 is close to an ISO 54. Swiss half sizes make it finer than the whole-millimetre ISO scale.
Worked example
Suppose you know you are a US 7:
- Inside diameter 17.3 mm
- Inside circumference 54.4 mm
- ISO / EU 54
- France 14
- Germany 17.3
- Switzerland 14.5
- UK N½
- Japan 14
All seven numbers describe one identical ring.
Rounding pitfalls
ISO sizes step in whole millimetres, which is coarser than a US quarter size. When converting from US quarter sizes you will sometimes land exactly between two European sizes. In that case, choose based on band width: round up for wide bands, down for very thin ones.
Buying across Europe
European jewellers are generally happy to quote inside diameter on request, and many stamp the size inside the shank. If a ring is stamped 54 it is ISO, if it is stamped 17.2 it is German, and if it is stamped 14 you need to ask whether that is French, Swiss or Japanese.
Use the converter to see all systems at once and quote the millimetre value when you order.