Oura Rolls Out Expanded Ring Sizing With New Ring 4 Kit

Fitting the size is easily the most important call when purchasing a smart ring, not least because Oura’s updated hardware makes that choice even more critical. With Ring 4 further expanding into the sizing spectrum and adjusting internal geometry, do not be surprised if your best fit is no longer the size you wore with Ring 3. Here’s a specialized, expert guide to finding your ideal Oura Ring size, for the best fit and most accurate health data.

How Being Fit is Important for Data Accuracy

Oura’s sensors depend on constant contact to record PPG signals of heart rate and HRV during sleep (and rest). A ring that moves around the finger or lifts away from the skin, which ramps up motion noise — possibly throwing off readings. On the other hand, an overly tight ring may hamper blood perfusion and influence the signal.

Independent sleep labs and university researchers that have tested smart rings agree that a snug, stable fit is crucial for matching gold-standard measures. Oura’s own validation documents have good agreement for nocturnal HR and HRV, when the device stays in firm contact during sleep.

Ring 3 vs. Ring 4 – Size Comparison and Fit Changes

Ring 4 comes with a new sizing kit ranging from sizes 4 to 15. And there are some changes in the internal design, too: the sensor bumps are a bit smaller and the inner geometry is more subtly altered. So a “size 8” in, say, Ring 4 may feel dissimilar from a “size 8” in Ring 3 on the same finger.

Ring 3’s kit includes sizes 6 to 13. According to measured samples, they are about 2.5–2.9 mm thick as well as just under 8 mm tall, but the thing that really makes them comfortable is internal diameter. Sliding the inner diameter even just slightly can cause a massive change in day-to-day feel.

Crucially, Oura does not offer half sizes, and its numbering doesn’t line up neatly with the numbers denoting standard US ring sizes. For example, a US size 6 usually corresponds to a 16.5 millimeter inner diameter, which is wider than Oura’s size 6. Charts are good for general context, but they’re ultimately no substitute for your finger and a set of sizers from Oura.

Picking the Best Finger and Orientation for Oura Rings

Oura advises best signal quality is from the index finger with the three sensor nubs oriented toward the palm. A tiny curve on the outside keeps it facing the right way at a glance. If index seems too weird, go with middle or ring finger — many long-timers there have refused to settle for a dip in data quality. The pinky is actually doable with Ring 4’s higher reach, but it is not the brand’s favorite choice.

Consider your dominant hand. The result is a better fit than wearing rings on bike-ride-bloated or post-yoga-swollen fingers, and there’s also less bumping and twisting during everyday tasks, ensuring the snug, stable grip that sensors crave.

How to Use the Oura Sizing Kit for an Accurate Fit

When you order, choose the sizer kit first for free. Oura ships the kit in advance of your ring so you can test a few sizes, confirm which one fits best, and finalize production. Ring 3 sizers are black, and Ring 4 sizers are white, so it’s easy to tell the difference between them.

Wear your top two as “finalists” for at least 24–48 hours. Fit can be experimented with during a workout, typing, dishwashing, and — most importantly — while you sleep overnight. The proper size goes over the knuckle with a little resistance, sits tight — no gaps! — and doesn’t spin. If it spins while your hands are dry, it’s too loose.

Size also varies by the hour depending on temperature and hydration. Jewelers often claim that arms/hands are smaller in the morning, but become larger throughout the day. Now is the time to try at different times, too, even after a hot shower and an evening walk. Opt for the smallest size that’s still comfortable in all situations.

If you can’t wait for a kit, Oura supplies official 3D print files for Ring 3 sizers, and there are also sizing kits available in major US retailers for both Ring 3 and Ring 4. Measuring the inner diameter of an existing ring can be useful, but real-world wear is a more reliable indicator than calipers by themselves.

Post-Delivery and Exchange Policy for Oura Ring Orders

If the final ring comes back as too loose or tight, Oura provides a one-time exchange in another size or color within its price point. Keep the device in good condition and within policy, and you will swap out quickly.

There will be slight variances between the plastic sizers and the final metal alloy ring. In practice, these differences are minimal, but if you’re on the edge, consider springing for all-day stability and nighttime comfort over a slightly looser daytime feel.

Quick Sizing Takeaways for Choosing Your Oura Ring Fit

Begin with the index finger, sensors facing toward the palm, and check fit throughout everyday activities as well as sleep. Ring 4 has a more generous 4–15 size range and redesigned interior, so you’ll want to double-check your size even if you have Ring 3. Ditch charts as the golden rule, bypass half-size logic, and it all comes down to fit.

Buy the smallest size that doesn’t rotate, confirm that it is comfortable when you are at your hottest and most active, and return for an exchange if the first try is off-base. Data — and your comfort — rely on it.