Ring Sizer Ring size conversion chart: US, UK, EU and Japanese sizes
Every country is measuring the same inside edge of the band, just labeling it differently. Run US 7 through Ring Sizer's converter and you get UK O, EU (Swiss) 14.00, JP 14.0 and a 17.20 mm diameter, and the Size Chart lists 61 sizes from 11.63 to 24.64 mm. The EU number has two flavors, which is the part that trips up most people ordering abroad.
Ring size chart in mm (US 5 to 10)
These rows are pulled straight from the app's Ring Size Chart, 61 sizes in quarter-size steps. The EU column here follows the inside circumference in millimetres, which is the version most European stores actually print.
| US | Inside diameter | UK | EU | JP |
|---|---|---|---|---|
| 5 | 15.70 mm | J ½ | 49 ¼ | 9 |
| 6 | 16.51 mm | L½ | 51 ¾ | 11 |
| 7 | 17.32 mm | N½ | 54½ | 14 |
| 8 | 18.14 mm | P½ | 57 | 16 |
| 9 | 18.95 mm | R½ | 59½ | 18 |
| 10 | 19.76 mm | T½ | 62 | 20 |
How to convert a ring size in the app
- Open System Converter from the home screen.
- Enter your size in the input field or use the slider.
- Under From, pick the system you know, for example US (American).
- Under To, pick the system you need: UK / AU, EU (Swiss), JP (Asian), Circumference (mm) or Diameter (mm).
- Read the converted size, then check All Equivalents to see every system at once.
- Tap Copy Result to paste the size into a shop's order form or a message.
Worked example: ring size US 7 to UK, EU and Japan
| System | Result |
|---|---|
| US | 7.00 |
| UK / AU | O |
| EU (Swiss) | 14.00 |
| JP (Asian) | 14.0 |
| Diameter | 17.20 mm |
| Circumference | 54.00 mm |
Why the chart and the converter can differ by half a size
This can be confusing at first glance. The converter snaps to the nearest row of a 28-row table, while the Size Chart reads from a finer 61-row table, so US 7 comes back as UK O and 17.20 mm in one place and N½ and 17.32 mm in the other — a 0.12 mm gap, under a quarter size, but enough to make it look like something's broken.
European sizing has its own split personality. The converter's EU (Swiss) option uses Swiss numbering, where US 7 is 14. Plenty of European shops instead print the inside circumference in mm, where the same ring is about 54. See a shop's sizes running in the 40s to 70s? That's circumference — switch the converter to Circumference (mm) or read the chart's EU column directly.
Comfort fit, wide bands and snug fit
The Fit Type picker under Comfort Fit Adjustment tacks an offset onto the converted size: Comfort Fit (+0.25), Wide Band (+0.5), Extra Wide (+1.0) or Snug Fit (-0.25). US 7 with Comfort Fit comes out as 7.25. Most people should leave this on Standard (no adjustment) unless the ring maker specifically says otherwise — their guidance always wins over a generic offset.
Tips for ordering from another country
- Convert from a measured diameter when you can; it is the one number every system agrees on.
- Check which EU style the shop uses before ordering.
- UK and Australian sizes use the same letters, with half sizes written as a letter plus ½.
- When a size falls between two rows, check the shop's own size guide too.
Questions and answers
What is ring size 7 in mm?
Can I convert a UK letter to a US size?
Is the full chart free?
What range does the converter accept?
You might also like
- Compare two ring sizes: how big is the difference? · Ring Sizer
More Ring Sizer guides
- How to measure your ring size at home with your phone
- Find a ring size without asking, a jeweler or a ring sizer
- Which finger to measure for your ring size
- Choosing a ring metal: gold, platinum, titanium and more
- Birthstone by month: a chart for all 12 months
- How to clean and care for a ring at home
- Compare two ring sizes: how big is the difference?
- Ring size in Mexico vs the US: how do you convert?
- Ring no longer goes over your knuckle: which size now?
- Does your ring size change during pregnancy, and how can you track it?
- All questions about Ring Sizer
- Back to Ring Sizer