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Comparison · 2 picks
Oura Ring 4 vs Circular Ring Slim (2026)
The Oura Ring 4 and the Circular Ring Slim sit at opposite ends of the smart-ring market: one is the accuracy benchmark with a subscription, the other is the slimmest no-subscription ring with a real accuracy caveat. This is not a close call for most buyers, but the right answer depends on what you value.
At a glance
All 2 options side by side.
 Oura Ring 4 |  Circular Ring Slim | |
|---|---|---|
| Best for | The better ring for almost everyone - category-leading accuracy and insights, if you accept the subscription. | A niche pick - choose it only if an ultra-slim profile and no subscription outweigh its accuracy compromises. |
| Check price | Check price |
The picks in detail
Oura Oura Ring 4
Bottom line. The better ring for almost everyone - category-leading accuracy and insights, if you accept the subscription.
Pros
- Sleep-stage and HRV accuracy repeatedly validated as closest to clinical testing
- Genuinely useful women's-health, metabolic and Resilience metrics
- Durable titanium with recessed sensors
- 4-7 day battery, ~80 min full charge
Cons
- Requires an Oura Membership (around 4.99 pounds/month) for most features
- No continuous SpO2 or always-on heart rate
- Data export is awkward - history is locked to the Oura app
Circular Circular Ring Slim
Bottom line. A niche pick - choose it only if an ultra-slim profile and no subscription outweigh its accuracy compromises.
Pros
- Slimmest smart ring on the UK market at 2.2mm
- No subscription required
- Temperature sensor at a sub-250-pound price
- Multi-LED PPG (IR, red, green)
Cons
- Tracking accuracy unreliable in multiple independent reviews
- Real-world battery 3-5 days, short of the claim
- App UX described as confusing by reviewers
- Exterior scratches easily; UK warranty routed via France
Which one should you buy?
For most people, the Oura Ring 4 is the stronger choice. Its sleep-stage and HRV algorithms are repeatedly validated as the closest to clinical testing, and its women's-health, metabolic and Resilience metrics are unmatched. The catch is the Oura Membership - around 4.99 pounds a month - which keeps the total cost rising for as long as you wear it.
The Circular Ring Slim answers the subscription objection and is the slimmest ring on the UK market at 2.2mm, with a temperature sensor under 250 pounds. But independent reviews repeatedly flag unreliable tracking accuracy, a confusing app and a finish that scratches easily. It is a niche pick rather than an all-rounder.
If your real motivation is avoiding a subscription, don't default to the Circular on price alone - the RingConn Gen 3 is a no-subscription ring with far more reliable data and a class-leading battery, and it is the comparison most no-subscription buyers should make.
How different is the accuracy?
This is the decisive gap. The Oura Ring 4 is the accuracy benchmark the rest of the category is measured against. The Circular Ring Slim, by contrast, draws repeated criticism in third-party testing for unreliable readings. If you are buying a ring to make decisions from the data - training load, recovery, sleep debt - that difference matters more than thickness or price. Remember that even the best smart ring produces trend data from finger-mounted optical sensors, so accuracy differences between models are real and worth weighting heavily.
When does the Circular actually make sense?
Three cases: you want the thinnest possible ring and find chunkier rings uncomfortable; you are firmly against any subscription and value the temperature sensor at the price; or you specifically prefer an EU-based manufacturer. Outside those, the accuracy and polish gap makes the Oura Ring 4 (for data quality) or the RingConn Gen 3 (for no-subscription value) the safer buy.