Ring Size Converter
Choose the sizing system you already know, select your size, and see the equivalent US, UK, and EU ring size along with the internal diameter and circumference in millimeters.
How It Works
Getting a ring size right matters more than most clothing sizes because a ring that is even slightly too tight or too loose is uncomfortable or risks slipping off and getting lost. This is especially important for engagement rings and gifts, where the person buying the ring often has to guess or convert a size from a hint rather than measuring the recipient's finger directly.
Ring size is based on the internal diameter and circumference of the band. This tool looks up your chosen size in a standard reference table and returns the matching size in every other system, since ring sizing is a matter of established convention rather than a single convertible formula.
Ring sizing can vary slightly by country and jeweler. These are standard, widely accepted reference values.
Reference Table
| US | UK | EU | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 3 | F | 44 | 14.1 | 44.2 |
| 3.5 | G | 45 | 14.5 | 45.5 |
| 4 | H | 46.5 | 14.9 | 46.8 |
| 4.5 | I | 47.5 | 15.3 | 48.0 |
| 5 | J | 49 | 15.7 | 49.3 |
| 5.5 | K | 50 | 16.1 | 50.6 |
| 6 | L | 51.5 | 16.5 | 51.9 |
| 6.5 | M | 52.5 | 16.9 | 53.1 |
| 7 | N | 54 | 17.3 | 54.4 |
| 7.5 | O | 55 | 17.7 | 55.7 |
| 8 | P | 56.5 | 18.1 | 57.0 |
| 8.5 | Q | 57.5 | 18.5 | 58.3 |
| 9 | R | 59 | 18.9 | 59.5 |
| 9.5 | S | 60 | 19.3 | 60.8 |
| 10 | T | 61.5 | 19.7 | 62.1 |
| 10.5 | U | 62.5 | 20.1 | 63.4 |
| 11 | V | 64 | 20.5 | 64.6 |
| 11.5 | W | 65.5 | 20.9 | 65.9 |
| 12 | X | 66.5 | 21.3 | 67.2 |
| 13 | Z | 69.5 | 22.2 | 69.7 |
Worked Example
A US ring size 7 has an internal diameter of about 17.3 millimeters and a circumference of about 54.4 millimeters, which corresponds to a UK size N and an EU size 54.
Frequently Asked Questions
How is ring size actually measured?
Ring size is based on the internal diameter or internal circumference of the band, that is, the measurement of the hole the finger goes through, not the outside of the ring.
Is a ring size chart the same in every country?
No. The US, UK, and EU use entirely different numbering systems for the same physical size, which is why a conversion table like this one is needed. Some countries also use their own local sizing standards not covered here.
Can I measure my ring size at home?
Yes. Wrap a strip of paper or string around your finger, mark where it overlaps, measure that length in millimeters, and compare it to the circumference column in the table.
Do ring sizes vary between jewelers?
Slightly. This table reflects standard, widely used reference values, but exact measurements can differ a little between jewelers and countries. When in doubt, get measured in person for an important purchase.
Why would I need to convert a ring size at all?
This comes up most often when buying an engagement ring or a gift while traveling or ordering from an overseas jeweler, when the only size you know is in a different system than the one the retailer uses.
Does finger size change during the day?
Yes, fingers can swell slightly with heat, activity, or time of day. For the most accurate size, measure in the evening when fingers tend to be at their largest, and avoid measuring right after exercise or in cold weather.