Ring sizes: converting between countries
The Spanish ring size equals the internal circumference of the ring in millimetres minus forty, so a band of fifty two millimetres circumference is a Spanish size twelve, a US size six and a UK size L and a half.
gelisted editorial team · Updated 15 August 2026
The short version
- Spanish size equals internal circumference in millimetres minus 40.
- The French system matches the Spanish one in practice.
- Fingers change volume by up to 4 per cent through the day.
- Resizing by one or two sizes costs 30 € to 90 €.
Buying a ring abroad or having one made means translating between systems that share neither scale nor logic. A table settles it in a glance.
How each system is built
Spain and France use the internal circumference in millimetres minus 40. The United States and Canada use their own numeric scale with half steps, derived from the internal diameter in inches. The United Kingdom uses letters of the alphabet. Germany and Switzerland state the internal diameter in millimetres directly. Mixing systems is the most common reason a commissioned ring does not fit.
| Circumference | Spain and France | United States | United Kingdom |
|---|---|---|---|
| 48 mm | 8 | 4,5 | I |
| 50 mm | 10 | 5,25 | K |
| 52 mm | 12 | 6 | L 1/2 |
| 54 mm | 14 | 6,75 | N |
| 56 mm | 16 | 7,5 | P |
| 58 mm | 18 | 8,25 | Q 1/2 |
| 60 mm | 20 | 9 | S |
| 62 mm | 22 | 10 | T 1/2 |
Measuring at home
With a ring already worn on the same finger, measure the internal diameter with a caliper or a ruler and multiply by 3,14 to obtain the circumference. Without a reference ring, wrap a paper strip 6 millimetres wide around the finger, mark where it closes and measure the length. That result is the circumference directly, and subtracting 40 gives the Spanish size.
When to measure
Mid afternoon and at a normal temperature. Fingers swell in heat, after meals and after exercise, with variations reaching 4 per cent of circumference, roughly half a size. Measuring first thing on a winter morning or straight after running in August produces results a full size apart. Where the choice lies between two sizes, take the larger one if the band is wide.
A band wider than 6 millimetres needs half a size more than a narrow one, because it covers more of the finger.
If it does not fit
Resizing by 1 or 2 sizes costs 30 € to 90 € and takes 3 to 7 days. Beyond 2 sizes the operation is more delicate, because it changes the proportions of the band and can affect the setting. Eternity bands set with stones all the way round, and rings in titanium or ceramic, cannot be resized at all: they have to be remade, starting from 150 €.
Frequently asked
+How is the Spanish size calculated?
By subtracting 40 from the internal circumference of the ring measured in millimetres.
+What US size matches a Spanish 12?
A size 6, corresponding to 52 millimetres of internal circumference.
+When should I measure the finger?
Mid afternoon at a normal temperature, since volume varies by up to 4 per cent through the day.
+Can I measure without a reference ring?
Yes, with a paper strip 6 millimetres wide wrapped round the finger and then measured.
+Can every ring be resized?
No. Eternity bands set all the way round and titanium or ceramic rings have to be remade.
Sources
- 1Gemological Institute of America, GIA (August 2026)
- 2Boletín Oficial del Estado, BOE (August 2026)