1. Design, Versions & Battery Life
  2. Health Monitoring and Sleep Tracking
  3. Smart and Fitness Features
  4. Prices and Subscriptions
  5. Which should you choose?

Oura Ring Gen 3 vs Circular Smart Ring Slim

Which smart ring is best? Here's our take
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The Oura Ring Gen 3 and Circular Ring Slim are both smart rings designed to help you track health and fitness more discreetly.

Oura has been around a bit longer than Circular and has established itself as the ring to beat.

We've spent time with both rings to get a better sense of what they offer, how they differ, and which one is the ring we'd choose to live with long-term.

Read on for our breakdown of how the Oura Ring Gen 3 compares to the Circular Ring Slim.

Reviewed: Oura Gen 3 review | Circular Ring Slim review

Design, Versions & Battery Life

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Both rings offer high-grade design aesthetics and attempt to offer the look and feel of wearing a normal stylish ring.

Starting with the Oura Ring Gen 3, it comes in either Heritage or Horizon designs. The Horizon offers a fully round design while the Heritage version has a flatter edge that sits on the top of your finger.

The Heritage comes in four different colors while the Horizon comes in six.

The Oura is made from titanium with a PVD coating and is water-resistant up to 100 meters, making it safe for swimming.

The Circular Ring Slim uses a mix of aluminum and carbon fiber and is suitable for showering and washing hands. Unlike the more expensive Circular Ring Pro, it comes in just a single black color.

Both require sizing kits, with the Oura offering sizes from US 6-13. It's the same size option as the Circular.

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In terms of looks, the Oura feels instantly more elegant than the two rings. It has the classier color options, and our silver Heritage version next to the black Circular ring, with its quite prominent logo on top, felt a little more basic in comparison.

Both are a good weight and unobtrusive to wear, but both are not immune to picking up scratches.

We've had the Circular for a shorter period, and it's already started to look quite scratched. Those scratches are less prominent on our silver Oura, but these are rings you do need to be mindful of activities where they might get rubbed against, like lifting weights, for instance.

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Battery setups on these rings do differ. While Oura opts for a charging cradle that you place the ring over, the Circular uses a USB-C portable charger that plugs directly into a USB-C port, like on a laptop port with the ring resting on the edge of it.

While the Circular charger is easier to clip onto your keys and carry around, the nature of plugging it in directly isn't always ideal in all charging scenarios.

In terms of battery, Oura claims you should enjoy up to seven days of battery life compared to up to five days on the Circular.

In reality, we've found it's less than that on both fronts. The Oura often maxes out around 3 days, while the Circular lasts two days in its most accurate performance mode.

There's also an eco mode, which will push things further but sacrifices letting you see sleep stage data and sample heart rate less frequently than when in performance mode.

Health Monitoring and Sleep Tracking

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Both Oura and the Circular Ring Air pack similar sensors and both require calibration periods to get the most reliable results.

For Circular, that period lasts 14 days while it's 30 days on the Oura Ring. Calibration ensures you get the most reliable heart rate tracking and temperature data overnight, with steady baselines for comparison to your normal day-to-day.

In terms of sensors, the Oura features an optical heart rate sensor and blood oxygen sensor, a skin temperature sensor, and an infrared sensor. The Circular includes the same sensors.

Oura uses those sensors primarily to power sleep tracking, which also influences its overarching Readiness insights, which take information like heart rate, heart rate variability, and body temperature to tell you how ready you are to take on your day.

The Circular breaks things down slightly differently. It also tracks your sleep, breaking down elements like sleep stages and captures metrics like heart rate variability, breathing rate, and SpO2 levels during the night. It also tracks stress levels and lets you take on-the-spot measurements of heart rate and SpO2.

Once you've completed the calibration period, you'll have access to Kira Plus, an assistant that offers suggestions based on your data and does offer useful suggestions for fitness tracking newcomers albeit it is slightly messy in its presentation of those suggestions.

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So there are different approaches to harnessing similar data points and metrics from similar sensor setups.

The core tracking experience is good across both of these rings. We'd say metrics like heart rate feel more accurate on the Circular, though sleep tracking, daily activity tracking, and Oura's more simple Readiness metric and overall more user-friendly app make it the nicer platform to interact with.

Smart and Fitness Features

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If you want these rings to track your fitness, then again, they take slightly different approaches.

The Circular ring uses the kind of accelerometer sensors found inside wrist-worn fitness trackers to track your daily steps and also score your cardio points and track activity intensity. There's no GPS or ability to pull in exercise data from other places to supplement what Circular offers. It does work with Apple Health and Google Fit.

Oura has a little more going on. It also uses similar sensors to track daily steps, can automatically recognize a range of exercises, offers a dedicated mode to track heart rate during exercise, uses its location settings to track routes, distance, pace, and speed, and also works with Strava, Google Fit, and Apple Health to use that data to better fuel recommendations and its Readiness metric.

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Outside of that tracking time, the Circular offers an alarm clock feature that sends vibrations to the ring, which you can stop by tapping on the logo on top of the ring. You also get a timer mode that can be set up inside the companion app.

Oura offers its Circles mode to follow the progress of fellow Oura users; it also includes sleep stories and meditations. Ultimately, both rings go pretty light on the kind of smart features you'd associate with smartwatches and fitness trackers.

Prices and Subscriptions

These rings aren't cheap, and if you opt for the Oura, things get more expensive thanks to the subscription you'll need to pay to get full access to all of the metrics available.

Prices for the Oura Ring start from $299 (~£182) or $349 (~£279) for the Heritage model (US prices only but available globally), and requires a $5.99 per month subscription ($6.99 outside of the US/EU).

The Circular Ring Slim costs $275/£220, so it's a tad cheaper in the US, but not if you include the mandatory ongoing cost.

Which should you choose?

There's no question that Oura is the most advanced and useful smart ring – and is one of the best wearables money can buy. But that's the main issue: it means spending more money than Circular thanks to the mandatory ongoing subscription.

The Circular Ring Slim wins out if you want a cheaper smart ring that offers a lighter design and a general overview of your health. Also, if you like the idea of the alarms and timers, it's a strong purchase.

But the Oura Gen 3 is a better-looking ring, more durable, and has more user-friendly app software. It's the superior ring in all departments.

It uses the metrics it collects together to offer simple calls to action, which makes it an excellent touch point for your daily health and wellness. What's more, Oura is a much richer health ecosystem, that's constantly being upgraded with new features and integrations.

Circular does have its Kira assistant, but it's hard to decipher the data and make it actionable.

The Circular Ring Slim is a good addition to the smart ring crowd but doesn't quite match up to Oura.

TAGGED Wearables

How we test

Michael Sawh


Michael Sawh has been covering the wearable tech industry since the very first Fitbit landed back in 2011. Previously the resident wearable tech expert at Trusted Reviews, he also marshaled the features section of T3.com.

He also regularly contributed to T3 magazine when they needed someone to talk about fitness trackers, running watches, headphones, tablets, and phones.

Michael writes for GQ, Wired, Coach Mag, Metro, MSN, BBC Focus, Stuff, TechRadar and has made several appearances on the BBC Travel Show to talk all things tech. 

Michael is a lover of all things sports and fitness-tech related, clocking up over 15 marathons and has put in serious hours in the pool all in the name of testing every fitness wearable going. Expect to see him with a minimum of two wearables at any given time.

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