Comparison · 2 picks
Oura Ring 4 vs Circular Ring Slim (2026)
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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.
 |  | |
|---|---|---|
| Price | £349 | See price |
| 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. |
| Review | Read review → | Read review → |
| Buy |
The picks in detail
Oura Ring 4
Bottom line. The better ring for almost everyone - category-leading accuracy and insights, if you accept the subscription.
Pros
- The most refined sleep-stage and HRV algorithms in the category, repeatedly validated against polysomnography in independent testing
- Titanium build with recessed PPG sensors that survive daily wear - most users report two-to-three years before noticeable scuffs
- Four-to-seven day battery in normal use, with a small, fast-charging puck included in the box
- Multiple sizes (US 6–13) and three finishes (Heritage, Stealth, Gold/Rose Gold) for fit and aesthetics
- Genuinely innovative women's-health and metabolic-load metrics that competitors are still catching up on
Cons
- Oura Membership at £5.99/month is required to access the bulk of features - it adds £71.88 to the first-year cost
- No always-on heart rate or live workout heart-rate broadcast - fitness use is supplementary rather than primary
- No continuous SpO2 reading - overnight SpO2 is a spot-check during sleep, not 24/7
- Higher-priced finishes (Stealth, Gold) command a £50–£200 premium for cosmetic differences only
- Closed ecosystem - your historical data lives inside the Oura app and is difficult to export in a portable form
More buying options (1)
- Oura Check price View deal →
Circular Ring Slim
Bottom line. A niche pick - choose it only if an ultra-slim profile and no subscription outweigh its accuracy compromises.
Pros
- 2.2mm thickness is the slimmest in the smart-ring category - most comfortable to wear
- No subscription required (differentiator vs Oura's £5.99/month)
- Temperature sensor (rare at this price tier - useful for cycle tracking + recovery)
- Multi-LED PPG (IR + red + green) for more comprehensive optical measurement
- French/EU manufacturer - some buyers value this over US-headquartered alternatives
Cons
- Multiple third-party reviews flag unreliable tracking accuracy vs Oura/Ultrahuman
- Exterior scratches easily per published reviews - cosmetic durability is a real issue
- Claimed 5-8 day battery rarely delivered in owners' real-world use (typical 3-5 days)
- App UX described as 'confusing' across multiple reviews
- UK warranty support via France-based parent is slower than UK-direct alternatives (Ultrahuman, RingConn)
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 5.99 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. Bear in mind Circular has since superseded the Slim with the Circular Ring 2, its current ring - if the Circular approach appeals, check that model first.
Frequently asked questions
Does the Oura Ring 4 really need a subscription?
Is the Circular Ring Slim accurate?
Which is the slimmest smart ring?
What if I want no subscription but reliable data?
See the full reviews
Read our in-depth verdicts before deciding.