Getting the right size for your Oura Ring Gen 4 matters more than for a standard piece of jewelry. The Gen 4 uses optical heart rate, skin temperature, and motion sensors on the underside of the band, and those sensors need consistent contact with the skin to produce accurate readings. A ring that is even slightly too large will rotate during sleep and activity, affecting the data the device collects.
This guide provides the complete Oura Ring Gen 4 size chart, explains how the sizes map to standard ring measurements, and walks through how to measure accurately before you order.
Oura Ring Gen 4 Size Chart
The Oura Ring Gen 4 is available in sizes 6 through 13, matching the same scale used for the Gen 3. Each size corresponds to a specific inner diameter in millimeters. The table below shows the size, inner diameter, and the approximate equivalent US and EU ring sizes for reference.
| Oura Size | Inner Diameter (mm) | Inner Circumference (mm) | Approx. US Size | Approx. EU Size |
|---|---|---|---|---|
| 6 | 16.5 | 51.8 | 6 | 52 |
| 7 | 17.3 | 54.4 | 7 | 54 |
| 8 | 18.2 | 57.2 | 8 | 57 |
| 9 | 19.0 | 59.7 | 9 | 60 |
| 10 | 19.8 | 62.2 | 10 | 62 |
| 11 | 20.6 | 64.7 | 11 | 65 |
| 12 | 21.4 | 67.2 | 12 | 67 |
| 13 | 22.2 | 69.7 | 13 | 70 |
How Oura Ring Gen 4 Sizing Differs from Standard Jewelry
The Oura Ring Gen 4 follows the same numerical size scale as standard US ring sizes in terms of the size labels, but the fit philosophy is different. A standard piece of jewelry is typically sized to sit comfortably with a small amount of movement. The Oura Ring is designed to sit snugly with minimal rotation to keep the sensors in contact with the underside of the finger at all times.
If you normally size jewelry with a little room to spare, you may need to size down by half a size when ordering the Oura Ring to achieve the snug fit the sensors require. Conversely, if your knuckle is significantly larger than the base of your finger, you will need to size for the knuckle and accept that the ring may move slightly at the base.
- Oura sizes 6 to 13 use the same scale as US ring sizes in terms of numbering
- The ring should fit snugly with minimal rotation, not loosely like casual jewelry
- Size down half a size from your usual jewelry size if you prefer a looser jewelry fit
- If knuckle-to-base difference is large, size for the knuckle and assess sensor contact
How to Measure for Oura Ring Gen 4 at Home
Before ordering, Oura recommends requesting their free sizing kit, which contains plastic sizing rings in all available sizes. Wearing the sizing ring for a full day is the most reliable way to confirm your size because you can assess how it feels through different activities, temperature changes, and overnight wear.
If you want a preliminary estimate before requesting the kit, measure the inner diameter of a ring that already fits snugly on your index or middle finger (the recommended fingers for Oura wear). Place the ring flat on a ruler and measure across the inner opening in millimeters. Match that measurement to the size chart above to find your starting size, then order the sizing kit to confirm before purchasing the actual device.
- Request Oura's free sizing kit before buying the ring
- Wear the sizing kit ring for a full day including sleep to assess the fit properly
- For a home estimate: measure inner diameter of a snug-fitting ring on the same finger
- Measure in the evening when fingers are at their largest
- If between sizes, start with the larger size kit ring and assess rotation
Which Finger Should You Wear the Oura Ring Gen 4 On?
Oura recommends wearing the Gen 4 on the index finger or middle finger of either hand for optimal sensor accuracy. These fingers provide a flatter underside surface than the ring finger, which can improve the consistency of blood flow readings. The ring finger is acceptable but may show slightly more reading variability for some users.
Whichever finger you choose, measure that specific finger for sizing. Ring size can differ by one to two full sizes between fingers on the same hand, so measuring a different finger and assuming it matches will often give you the wrong size.
Oura Ring Gen 4 vs Gen 3: Size Compatibility
The Oura Ring Gen 4 uses the same size scale as the Gen 3, ranging from size 6 to size 13 with the same inner diameter measurements at each size. If you already know your Gen 3 size and it fit well, you can order the same size for the Gen 4 without re-measuring.
The Gen 4 is slightly thinner and lighter than the Gen 3, which may make the same size feel marginally less snug for some wearers. If your Gen 3 ring felt borderline loose, consider sizing down by one size for the Gen 4 to maintain the same level of sensor contact.
- Gen 4 and Gen 3 use the same size scale (6 to 13)
- Same size number = same inner diameter across generations
- Gen 4 is slightly thinner and lighter than Gen 3
- If Gen 3 felt borderline loose, try one size smaller for Gen 4
Use Our Ring Size Calculator
Our free ring size calculator helps you convert an inner diameter or circumference measurement into the corresponding size across US, UK, EU, and India systems. If you have measured a ring that fits your index finger at home, enter the inner diameter to find your starting Oura Ring Gen 4 size.
For a broader guide to smart ring sizing principles, see our Oura Ring size guide. For guidance on whether Oura uses the same scale as standard ring sizing, see is Oura Ring size standard.
FAQ
What sizes does the Oura Ring Gen 4 come in?
The Oura Ring Gen 4 is available in sizes 6 through 13, the same range as the Gen 3. Each size corresponds to a specific inner diameter, ranging from 16.5 mm at size 6 to 22.2 mm at size 13. Oura provides a free sizing kit to help you confirm your size before purchasing.
Is the Oura Ring Gen 4 the same size as the Gen 3?
Yes. The Gen 4 uses the same size scale and inner diameter measurements as the Gen 3. If you wore a Gen 3 at size 8, for example, you can order a Gen 4 size 8 as your starting point. The Gen 4 is slightly thinner and lighter, so if your Gen 3 felt borderline loose, consider sizing down one size for the Gen 4.
How do I find my Oura Ring Gen 4 size?
The most reliable method is to request Oura's free sizing kit and wear the plastic sizing rings for a full day before ordering. For a preliminary estimate, measure the inner diameter of a ring that fits snugly on the finger you plan to wear the Oura on, then match the measurement to the size chart above.
Should I size up or down for the Oura Ring Gen 4 compared to my jewelry size?
If your jewelry rings fit with a comfortable amount of movement, consider sizing down by half a size for the Oura Ring Gen 4 to achieve the snug fit the sensors need. If your jewelry rings already fit snugly with minimal rotation, your usual size is a good starting point. Always confirm with the sizing kit before ordering.
What finger should the Oura Ring Gen 4 be worn on?
Oura recommends the index or middle finger on either hand for the most consistent sensor readings. The ring finger is also acceptable. Whichever finger you choose, measure that specific finger for sizing because ring size varies significantly between fingers.
