Swiss, German and French ring sizes describe the same ring with different numbers. French sizes follow ISO 8653 and equal the inner circumference in mm. Swiss and Italian sizes are the circumference minus 40 mm. German sizes are the inner diameter in mm. A ring with a 54.4 mm circumference is French 54, Swiss 14.4 and German 17.3.
How Each System Is Defined
| System | What the number is | Example: US 7 ring |
|---|---|---|
| French / EU (ISO 8653) | Inner circumference in mm | 54 |
| Swiss and Italian | Inner circumference minus 40 mm | 14.4 |
| German | Inner diameter in mm | 17.3 |
| US | Steps of about 0.81 mm of diameter | 7 |
| UK and Australia | Letters with half steps | N½ |
Wikipedia reports that Swiss size 10 equals ISO size 50, that the German system is used in Germany and the Netherlands, and that France uses the ISO system. Japan uses a numeric scale that is not linear in either diameter or circumference, so read it from a chart.
The Same Ring in Five Systems
A ring with an inner diameter of 17.32 mm has a circumference of 54.4 mm. It gets a different number in each system.
[INFOGRAPHIC: insert infographic_same_ring_five_systems.webp]
Alt text: One ring of 54.4 mm circumference labelled French 54, Swiss 14.4, German 17.3, US 7 and UK N½
Caption: One ring, five size numbers.
Conversion Chart: US, UK, French, Swiss and German
| US size | UK size | French / EU | Swiss / Italian | German (diameter mm) |
|---|---|---|---|---|
| 5 | J½ | 49 | 9.3 | 15.7 |
| 5.5 | K½ | 51 | 10.6 | 16.1 |
| 6 | L½ | 52 | 11.9 | 16.5 |
| 6.5 | M½ | 53 | 13.1 | 16.9 |
| 7 | N½ | 54 | 14.4 | 17.3 |
| 7.5 | O½ | 56 | 15.7 | 17.7 |
| 8 | P½ | 57 | 17.0 | 18.1 |
| 8.5 | Q½ | 58 | 18.2 | 18.5 |
| 9 | R½ | 60 | 19.5 | 18.9 |
| 9.5 | S½ | 61 | 20.8 | 19.4 |
| 10 | T½ | 62 | 22.1 | 19.8 |
| 11 | V½ | 65 | 24.6 | 20.6 |
Swiss values are the exact circumference minus 40, so shops that round will show whole numbers such as 14 for 14.4. For a full conversion list, see the Swiss ring size chart and the ring size conversion chart.
Why Shops Give You Different Numbers
Each shop uses the system of the country where the brand sits. An Italian brand such as Gucci numbers by the Italian rule, a Swiss or Italian jeweller subtracts 40 mm, a German shop quotes a diameter, and a French or EU shop quotes the circumference. A German size of 17 and a French size of 54 describe nearly the same ring, but 17 and 54 look unrelated. Always check which system a chart uses before you convert. For a worked brand example, read do Gucci rings run big or small.
How to Convert Between Systems
- Find the inner circumference in mm. Multiply a German diameter by 3.1416, add 40 to a Swiss number, or use the French number directly.
- Read the circumference in the chart above, or use the mm to ring size chart.
- Check UK letters in the UK to EU ring size chart.
- If your result falls between sizes, read finding the perfect fit in between ring sizes.
Frequently Asked Questions
How do I convert a Swiss ring size to a US size?
Add 40 to the Swiss number to get the circumference in mm, then match it to the chart. Swiss 14.4 is 54.4 mm, which is US 7.
Is a Swiss size the same as an EU size?
No. A Swiss size is the EU circumference minus 40. Swiss 10 equals EU 50.
What is the difference between German and French sizes?
German sizes are the inner diameter in mm. French sizes are the inner circumference in mm, so French is about 3.14 times the German number.
Are Italian and Swiss ring sizes the same?
Wikipedia describes both as the circumference minus 40 mm.
Why does my ring size look so different in each country?
Because the systems measure different things: circumference, circumference minus 40, diameter or letter steps.
Source: Wikipedia: Ring size.