Oura Ring sizes run on the US whole-size scale, from 4 to 15 depending on the generation. If you know your ring size in UK or EU sizing, or you've only ever measured in millimeters, this chart converts between all four.
Honest caveat: only the US and mm columns are precise. UK and EU equivalents are estimates, since Oura doesn't publish official conversions for those systems. For complete step-by-step sizing rules, refer to our primary Oura Ring size guide.
If you haven't measured your finger yet, use the sizing calculator or the wrap-and-measure method from the main size guide before referencing this chart.
Once you have a circumference measurement in millimeters, find the closest row below and read across.
If you already own jewelry in a UK or EU size that fits the target finger well, work backward: find that size in the table and read the corresponding US column.
Treat the result as a strong starting point, not a final answer — Oura's interior sensor housing changes the fit relationship compared to a flat band. Understanding why Oura sizing is different will help explain why standard rings don't convert identically.
Rows highlighted in gold fall within Oura Ring 5's available range (US 6–13). The full table reflects Oura Ring 4's wider range (US 4–15).
| US Size | Circumference (mm) | EU | UK / Ireland |
|---|---|---|---|
| 4 | 46.8 | 46 | H |
| 4.5 | 47.8 | 47 | I |
| 5 | 49.1 | 49 | J½ |
| 5.5 | 50.3 | 50 | K½ |
| 6 | 51.5 | 51 | L |
| 6.5 | 52.8 | 52 | M½ |
| 7 | 54.0 | 54 | N½ |
| 7.5 | 55.3 | 55 | O½ |
| 8 | 56.6 | 57 | Q |
| 8.5 | 57.8 | 57 | R½ |
| 9 | 59.1 | 59 | S½ |
| 9.5 | 60.3 | 60 | T½ |
| 10 | 61.6 | 62 | U½ |
| 10.5 | 62.9 | 62 | V½ |
| 11 | 64.1 | 64 | X |
| 11.5 | 65.4 | 65 | Y |
| 12 | 66.6 | 67 | Z |
| 12.5 | 67.9 | 67 | Z+1 |
| 13 | 69.1 | 69 | Z+3 |
| 13.5 | 70.4 | 70 | Varies by retailer |
| 14 | 71.7 | 71 | Varies by retailer |
| 14.5 | 72.9 | 72 | Varies by retailer |
| 15 | 74.2 | 74 | Varies by retailer |
UK equivalents above size 13 aren't shown as specific letters because ring sizing convention beyond "Z" isn't standardized — different jewelers extend the scale differently, with no universal agreement on the increment. If you're in that range, use the US size or millimeter measurement instead, since those stay precise at any size.
The two generations don't fit identically at the same nominal size, since Ring 5 has a redesigned, slimmer interior.
If you're converting a Ring 4 size forward to Ring 5, treat this chart as a starting reference and re-measure rather than assuming an exact carryover. Our separate Ring 4 vs Ring 5 sizing guide covers this in more depth.
Standard ring-sizing conversion tables vary slightly between sources — there's no single universal international standard, the way there is for shoe sizing in some regions.
It's the only measurement that doesn't depend on different conversion conventions. EU sizes closely match millimeter measurements by design — that's why the EU column aligns so closely with the mm values.
Find your US size or millimeter measurement in the chart above and read across to the UK column. Note that UK equivalents above US size 13 aren't standardized across retailers, so treat those rows as rough estimates only.
EU ring sizes closely track the circumference measurement in millimeters, so the EU column in the chart above is generally the most reliable of the three converted columns.
The millimeter circumference is measured the same way, but Oura's interior sensor housing can change how a given circumference actually feels compared to a flat standard band. Use the mm figure as a starting point, then confirm with a physical sizer.
Ring sizing conventions beyond UK size "Z" aren't standardized — different jewelers extend the letter scale in different ways. We'd rather leave it blank than publish a specific letter that might not match what a given retailer uses.
They're the same conversion chart, but Oura Ring 5 is only available in sizes 6 through 13, while Ring 4 covers 4 through 15. Check which generation you're ordering before you finalize a size outside the 6–13 range. If you select the wrong size after ordering, check the Oura Ring return policy for wrong size to review your replacement process.