Oura Ring 4 vs Circular Ring 2 — which smart ring rules them all?

I’m currently testing the Circular Ring 2, a subscription-optional smart ring that boasts eight days of battery, ECG readings, AFib detection, and a revolutionary new digital sizing process. While the jury is still out on its data accuracy, my initial impressions of the Circular Ring 2 are positive.

Of course, when assessing what could be one of the best smart rings in 2025, it’s impossible not to compare it to the Oura Ring 4, our hands-down favorite finger wearable available right now.

While this comparison is subject to updates based on the results of further testing, here’s how the Oura Ring 4 versus Circular Ring 2 plays out across six categories, including price, sizes and finishes, design and durability, health features, fitness features, and battery life.

Oura Ring 4 vs Circular Ring 2: Specs compared

Oura Ring 4 vs Circular Ring 2: Price

The Oura Ring 4 starts at $349 and requires a $5.99 monthly subscription for the Oura app.

The Circular Ring 2 also starts at $349 and is subscription-free for most features. However, forthcoming tools, including blood pressure and blood glucose monitoring, are likely to be locked behind a paywall. This has understandably frustrated early backers of the Circular Ring 2, which launched earlier this year on Kickstarter and was billed as completely subscription-free.

In Circular’s defense, the to-be-paywalled features were never part of the original pitch, but rather, "stretch goals" for the device. No word yet on what access to blood pressure and glucose monitoring will cost, or when either will debut; the Circular site says late 2025 for the former and early 2026 for the latter.

Still, with the majority of its core features free for all users, the Circular Ring 2 wins this category.

Winner: Circular Ring 2

Oura Ring 4 vs Circular Ring 2: Sizes and finishes

The Oura Ring 4 is available in sizes 4 through 15 and the following finishes: Gold, Rose Gold, Silver, Brushed Titanium, Black, and Stealth. The Circular Ring 2 comes in sizes 6 through 14 in your choice of Gold, Rose Gold, Black, or Silver.

Though Circular offers its device in fewer sizes and finishes, the brand’s pre-purchase sizing process is far superior to Oura’s. Even though Circular continues to offer a physical sizing kit — check out a video of me demoing it at CES — the Circular Ring 2 can be sized using just the Circular app. Oura, meanwhile, mails a kit of plastic dummy rings for sizing.

Winner: Draw

Oura Ring 4 vs Circular Ring 2: Design and druability

Both smart rings boast an all-titanium exterior. That said, the exterior of the Circular Ring 2 seems more susceptible to scratches, and that's based on just one week of wear.

The Oura Ring 4 is more comfortable than the Circular Ring 2, thanks to recessed sensors. The Circular Ring 2 isn’t uncomfortable, but the protruding interior sensors do leave an indentation on my finger.

The Circular Ring 2 is a little heavier than the Oura Ring 4, but the difference is fairly negligible. Durability-wise, the Circular Ring 2 is IP68 rated against moisture and dust. This means you can wear it in the shower or while washing your hands without worry. However, it’s not rated for swimming. The Oura Ring 4, on the other hand, is rated for 50 meters of water resistance, so you can swim with it on.

Winner: Oura Ring 4

Oura Ring 4 vs Circular Ring 2: Health features

Both smart rings have onboard heart rate, blood oxygen, and body temperature sensors, along with accelerometers to monitor movement. While the Oura Ring 4 is the gold standard for accurate holistic data from a smart ring, Circular’s data also looks promising.

Both apps offer insights into your vitals, sleep quality, and energy levels. They each also offer women’s health tracking features. However, Oura’s insights go into more detail than Circular’s, while providing a wider range of tracked metrics.

That said, only the Circular Ring 2 offers ECG readings and AFib detection. Still, for having a more comprehensive approach to holistic data, I'm giving the Oura Ring 4 the win in this category.

Winner: Oura Ring 4

Oura Ring 4 vs Circular Ring 2: Fitness features

While the Circular Ring 2 offers a daily Energy Score that’s similar to Oura’s Readiness Score, the Oura Ring 4 is better suited for activity tracking. Neither device has an onboard GPS, so you’ll need to carry your phone with you while working out for location, pace, distance, etc. data, but the Oura Ring 4 can automatically detect and track up to 40 different workout types.

The Circular Ring 2, meanwhile, can automatically detect a few basic workouts like walking and running, but not more astute pastimes like badminton or horseback riding. You know what smart ring can? The Oura Ring 4.

Winner: Oura Ring 4

Oura Ring 4 vs Circular Ring 2: Battery life

The Oura Ring 4 and Circular Ring 4 both advertised eight days of battery per charge. In our testing, the Oura Ring 4 lasts a little closer to six days per charge. Though I’m still testing the Circular Ring 2, real-world battery life appears to be slightly better, at seven days per charge.

The Circular Ring 2 has another advantage over the Oura Ring 4: It ships with a travel-friendly, battery-sporting charging case, which can recharge the ring to 100% in just 30 minutes.

Winner: Circular Ring 2

Oura Ring 4 vs Circular Ring 2: Overall winner

The Oura Ring 4 and Circular Ring 2 cost the same up front, $350, but the Oura Ring costs more in the long run due to the mandatory $5.99 monthly subscription. Even still, the Oura Ring 4 is the better overall smart ring than the Circular Ring 2, thanks to a more durable design, more comprehensive wellness insights, better fitness tracking, and greater size availability.

Still, the Circular Ring 2 has the upper hand when it comes to battery life and heart health monitoring, thanks to its ability to perform ECG readings and detect potential AFib. That said, I wouldn’t be at all surprised if these features eventually came to the Oura Ring, either by way of a firmware update or an Oura Ring 5.

Overall winner: Oura Ring 4

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