The Gemological Institute of America’s (GIA) chart pairs US 7 with UK N, at an inside diameter of 17.3 mm and an inside circumference of 54.3 mm. UK letters and US numbers are not treated as perfectly interchangeable: check the millimetre measurements and the intended sizing system with your jeweller.
US to UK ring size conversion chart
This table follows GIA’s international ring size chart and measuring guidance. It includes quarter sizes so you can see the millimetre differences rather than relying on rounded equivalents.
| Inside diameter (mm) | Inside circumference (mm) | US / Canada | UK / Australia |
|---|---|---|---|
| 14.1 | 44.3 | 3 | F |
| 14.3 | 44.9 | 3¼ | F½ |
| 14.5 | 45.6 | 3½ | G |
| 14.7 | 46.2 | 3¾ | G½ |
| 14.9 | 46.8 | 4 | H |
| 15.1 | 47.4 | 4¼ | H½ |
| 15.3 | 48.1 | 4½ | I |
| 15.5 | 48.7 | 4¾ | I½ |
| 15.7 | 49.3 | 5 | J |
| 15.9 | 50.0 | 5¼ | J½ |
| 16.1 | 50.6 | 5½ | K |
| 16.3 | 51.2 | 5¾ | K½ |
| 16.5 | 51.8 | 6 | L |
| 16.7 | 52.5 | 6¼ | L½ |
| 16.9 | 53.1 | 6½ | M |
| 17.1 | 53.7 | 6¾ | M½ |
| 17.3 | 54.3 | 7 | N |
| 17.5 | 55.0 | 7¼ | N½ |
| 17.7 | 55.6 | 7½ | O |
| 17.9 | 56.2 | 7¾ | O½ |
| 18.1 | 56.9 | 8 | P |
| 18.3 | 57.5 | 8¼ | P½ |
| 18.5 | 58.1 | 8½ | Q |
| 18.8 | 59.1 | 8¾ | Q½ |
| 19.0 | 59.7 | 9 | R |
| 19.2 | 60.3 | 9¼ | R½ |
| 19.4 | 60.9 | 9½ | S |
| 19.6 | 61.6 | 9¾ | S½ |
| 19.8 | 62.2 | 10 | T |
| 20.0 | 62.8 | 10¼ | T½ |
| 20.2 | 63.5 | 10½ | U |
| 20.4 | 64.1 | 10¾ | U½ |
| 20.6 | 64.7 | 11 | V |
| 20.8 | 65.3 | 11¼ | V½ |
| 21.0 | 66.0 | 11½ | W |
| 21.2 | 66.6 | 11¾ | W½ |
| 21.4 | 67.2 | 12 | X |
| 21.6 | 67.9 | 12¼ | X½ |
| 21.8 | 68.5 | 12½ | Y |
| 22.0 | 69.1 | 12¾ | Z |
| 22.2 | 69.7 | 13 | Z½ |
For example, US 6 sits alongside UK L at 16.5 mm in this chart. Some simpler charts give 16.4 mm for US 6. That detail matters when you are ordering to a half size, which is why we have recorded the source rather than blending different tables.
Why UK letters and US numbers do not line up neatly
The UK system uses letters, with half sizes. GIA’s US chart commonly progresses in quarter steps. Each letter covers two quarter steps on this GIA chart, but different published charts can place their letter labels against slightly different millimetre measurements. Keep the millimetre measurement and its source with your size so the comparison is clear.
Measure the ring, then consider its fit
For an existing round ring, GIA recommends reading it on a marked ring mandrel. For an even-width ring, the size is read where the central point of the band’s width touches the mandrel. A digital calliper can provide an inside diameter reference, but reading a tapered band requires a standard measuring method.
To measure your finger, use a sizing gauge similar in width to the intended ring. It should pass over the finger joint without being forced, then sit comfortably where you will wear it. Temperature and time of day can affect how a finger measures, so a quick reading on one occasion is not a complete fitting.
Wider rings generally fit more snugly. GIA advises wide-finger sizing gauges for rings over 4 mm wide. Instead of automatically adding a size, ask for a fitting with a comparable gauge.
What to send for a bespoke ring
Tell us the actual finger and hand, the inside diameter or circumference you measured, and which letter or number you were given. Include the band width, whether the ring has a comfort fit interior and the date you checked the fit. This lets us discuss any uncertainty before you approve your design.
You may find the full ring sizing guide useful for its international comparisons. For more detail on the difference between measuring across a ring and around your finger, see how millimetres relate to ring size. If you are unsure which reading applies, send us your measurements.
Frequently asked questions
What UK size is a US 7?
In GIA’s international ring size chart, US 7 corresponds to UK N, with an inside diameter of 17.3 mm and an inside circumference of 54.3 mm. Ask your jeweller to confirm this using the sizing system for the ring being made.
What UK size is a US 9?
In GIA’s international ring size chart, US 9 corresponds to UK R, with an inside diameter of 19.0 mm and an inside circumference of 59.7 mm.
Why do UK letters not always match whole US sizes?
The scales advance at different intervals. On this GIA chart, one UK letter covers two US quarter-size steps. A UK half letter matches a whole or half US size on this table, rather than sitting between its quarter-size steps. Other published charts can align their labels differently.
Is a conversion chart enough to choose my final size?
A chart is a useful comparison, not a final fitting. Confirm the finger, ring width and sizing system with your jeweller before the ring is made.