Ring Size Conversion Chart: US, UK, EU and Millimetres
Start With the Measurement and the Sizing System
A ring size is useful only when you know which system it uses. For a Singapore fitting, bring the original size label, the jeweller's sizing system and, if available, the ring's inside diameter or circumference in millimetres. Diameter is the distance across the inside of the ring; circumference is the distance around it. They are different measurements.
US sizes use numbers and UK sizes use letters. Many European retailers use circumference-based size numbers, but conventions and rounding vary. Treat a conversion as a starting point and confirm the fit on the intended finger with a gauge similar in width to the finished ring.
Conversion Chart
| US / Canada | UK reference | Inside diameter mm | Inside circumference mm |
|---|---|---|---|
| 4 | H | 14.9 | 46.8 |
| 5 | J | 15.7 | 49.3 |
| 6 | L | 16.5 | 51.8 |
| 6½ | M | 16.9 | 53.1 |
| 7 | N | 17.3 | 54.3 |
| 7½ | O | 17.7 | 55.6 |
| 8 | P | 18.1 | 56.9 |
| 8½ | Q | 18.5 | 58.1 |
| 9 | R | 19.0 | 59.7 |
| 9½ | S | 19.4 | 60.9 |
| 10 | T | 19.8 | 62.2 |
| 11 | V | 20.6 | 64.7 |
| 12 | X | 21.4 | 67.2 |
These selected rows follow the GIA international chart. They are approximate reference conversions, not a universal manufacturing specification. Other jewellers may map a US size to a different UK half-size or round the millimetre values differently.
For circumference-based European sizing, use the circumference column as the measurement to discuss with the retailer. For example, around 52 mm circumference is near an EU 52 label, subject to that retailer's convention. Do not enter a diameter such as 16.5 mm as an EU size.
How to Use a Measurement at Home
From a ring that already fits: measure straight across its inside centre, excluding the metal, and use the inside-diameter column. The ring should be round and normally worn on the intended finger. A distorted ring or a measurement from a different finger is a poor guide.
From a paper or string measurement: the measured length is an approximate circumference, not a diameter. Stretch, paper damage, the tightness of the wrap and the knuckle can all affect the result. Use this only for an initial conversation, not as the final size for making a ring.
Small measurement errors matter. If you can, bring the existing ring to a jeweller or have the intended finger measured with proper gauges before committing to the size.
What Changes the Size You Actually Need
Band width: wider bands and several rings worn together can feel tighter. Try a gauge comparable to the finished band or complete stack rather than automatically adding half a size.
Temperature: fingers shrink in cold and swell in heat — measure at normal room temperature, not right after being outdoors in extreme weather.
Time of day: fingers are typically largest later in the day, so measuring in the evening gives the most reliable everyday-wear result.
The knuckle: a ring has to clear it. If your knuckle is noticeably wider than the base of your finger, measure both and choose a size that balances comfort against the risk of it slipping off.
Dominant hand: typically runs slightly larger than the other hand — always measure the specific hand and finger the ring will actually be worn on.
If you are between sizes, compare both with your jeweller. The ring needs to clear the knuckle without slipping off during normal wear. Confirm any future resizing options before ordering, especially for full-eternity, pavé or intricate designs. A loose fit should not be accepted on the assumption that every ring can simply be resized down.
Further Reading
Contact Diamond Ateliers to arrange a fitting and discuss the ring or stack you plan to wear.
Common Questions
How do I convert my US ring size to UK or EU?
Use a chart that identifies its convention, then confirm the result with the jeweller making the ring. US, UK and circumference-based European labels are approximate equivalents, not interchangeable specifications.
What is the most universal ring size measurement?
Inside diameter and inside circumference in millimetres are physical measurements. Always say which one you have measured; a diameter of 16.5 mm is not a circumference of 16.5 mm.
Can I measure my ring size at home without a sizer?
An existing ring can provide an initial estimate. Paper and string measurements are less reliable. Have the intended finger checked with a suitable sizing gauge before finalising a bespoke ring.