BRAND GUIDE
Oura Ring size guide
Why a smart ring can't use a normal size chart
Oura's band is roughly 7 to 8mm wide, more than double the width of a typical thin fashion ring, and it needs to sit snugly enough for its sensors to stay in steady contact with the skin. Both of those push Oura's sizing away from standard jewelry sizing: a wider band already needs a size adjustment on its own, on top of the tighter, sensor-driven fit Oura is aiming for. Oura sizes in whole numbers only, with no half sizes, and explicitly recommends against sizing from a regular ring you already own for that reason.
Approximate conversion, for a starting estimate only
Use this to guess which sizes to request in a free Oura sizing kit, not as a final answer, and compare against the full ring size chart for other regions.
| Oura size | Roughly equivalent US size | Diameter (mm) |
|---|---|---|
| 6 | 6 | 16.5 |
| 7 | 7 | 17.3 |
| 8 | 8 | 18.1 |
| 9 | 9 | 18.9 |
| 10 | 10 – 10.5 | 19.8 |
| 11 | 11 – 11.5 | 20.6 |
| 12 | 12 | 21.4 |
| 13 | 12.5 – 13 | 21.8 |
Which finger and hand
Oura's own guidance favors the index, middle, or ring finger for the most reliable sensor contact, on either hand, and specifically advises against the little finger, since it swells and shrinks more than other fingers and gives noisier readings. If your knuckle is noticeably wider than the base of the finger you're sizing, expect the fit to feel different from a thin ring at the same numeric size, the width alone will make it sit tighter over the knuckle.
Between two sizes
If a sizing kit ring feels right in the moment but slightly loose after a few hours, or slightly tight in the morning after wearing it overnight, that's a normal daily swelling range, not a sign the size is wrong. Oura recommends wearing a sizer for a full 24 hours, including sleep, before deciding, precisely because a five-minute test misses that swing.