Inside the Oura Ring 4: Sensors, Battery, App, and Subscription

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This article is for general information only and is not medical advice. Readers should consult a qualified healthcare provider for diagnosis or treatment.

The Oura Ring 4 is the smallest and most comfortable ring Oura has ever made, and it’s also the most expensive way to get into smart rings if you count the membership. Here’s what’s actually inside the hardware, what the app gives you for the monthly fee, and where the trade-offs are. No hand-wave verdicts — just the spec sheet broken down in plain English.

Sensors

Oura Ring 4 is a fully titanium body with a fully round interior — no nubs, no bumps, no plastic insert that one previous generation famously had. The sensors live recessed inside the ring and contact your finger from the bottom of the band:

• Optical heart rate (PPG): green and infrared LEDs that read pulse continuously through the day and night.
• Pulse oximetry (SpO2): red and infrared LEDs read blood oxygen during sleep.
• Skin temperature: a contact thermometer that captures overnight temperature deviation from your personal baseline.
• Accelerometer: 3-axis motion sensor for activity classification, automatic workout detection, and sleep staging.

Oura Ring 4 introduces what they call Smart Sensing, which dynamically adjusts which LEDs are active based on signal quality on your specific finger. It’s a way to claw back battery without losing read accuracy.

Design and dimensions

The numbers off the official spec sheet:

• Width: 7.90mm
• Thickness: 2.88mm
• Weight: 3.3 to 5.2 grams, depending on ring size
• Material: titanium throughout, including the inner surface
• Sizes: 4 through 15 (a wider range than most competitors, including Gen 3)
• Finishes: Silver, Black, Brushed Silver, Stealth, Gold, Rose Gold

The fully round interior is the under-discussed upgrade from Gen 3. If you’ve worn a Gen 3 and felt the sensor cluster pressing into your finger, Ring 4 is built specifically to fix that.

Battery life

Oura quotes 5–8 days of battery, with the spread depending on ring size (smaller ring = smaller battery) and on how aggressively you use the live features. Charge time is roughly 20–80 minutes depending on how depleted the battery is. The charger is size-specific and ships with the ring.

In practice, Ring 4 lands at the same battery life as Gen 3 — Oura traded what could have been longer life for the slimmer and more comfortable design. If maximum runtime is your priority, this isn’t the ring.

Water resistance

Rated for typical daily wear including handwashing, showering, and swimming. Oura’s marketing language is conservative on saunas and deep diving — the ring is fine for normal water exposure but not for sustained high-temperature or high-pressure environments.

The Oura app and the membership

The hardware is half the product. The Oura app is where the numbers turn into the daily Sleep Score, Readiness Score, Activity Score, and the cycle-tracking and stress features that get most of the marketing attention. It’s also where the recurring fee lives.

An Oura Membership runs roughly $5.99 per month (or yearly equivalent), and it gates almost everything you’d buy the ring for: detailed sleep stages, daily scores, cycle insights, the Resilience trend, and the personal coaching content. Without a membership the ring still tracks data and the app shows raw heart rate, steps, and skin temperature, but you lose the daily insights that justify the price tag.

App compatibility is broad: iOS 16+ and Android 10+, with Apple Health and Google Health Connect integration. Oura also integrates with Strava, Garmin, Natural Cycles, Flo, Clue, and a long list of fitness and women’s-health apps.

Subscription model: pay-monthly or pay-once

You buy the ring outright (starts around $349 for Silver, climbing for premium finishes) and then pay the membership separately. There’s no “buy once” path that unlocks the daily scores. If you’re allergic to subscriptions on principle, this is the friction point — and it’s the wedge that competitors like Ultrahuman, RingConn, and Samsung use to win price-sensitive buyers.

Who should buy the Oura Ring 4

People who want the cleanest sleep and recovery data on the market and don’t mind paying for it month after month. The published research base is the deepest of any consumer ring, the algorithms have been refined over multiple generations, and the app is the most polished. If sleep tracking is the single biggest reason you’re considering a ring, this is the safe answer — even if it’s also the most expensive.

Who should skip it

People who reject subscriptions on principle, people on a strict budget, and people who already own a Samsung phone and would get most of the same metrics through Galaxy Ring‘s no-subscription Samsung Health integration. If glucose or metabolic health is your specific interest, Ultrahuman’s heavier metabolic framing may fit better.

The bottom line

Oura Ring 4 is the most refined hardware in the category, paired with the most polished app and the highest total cost of ownership. The titanium build is excellent, the size range is the widest available, and the daily insights are the best in class — but the membership is non-negotiable if you actually want those insights. Decide whether you’re comfortable paying a recurring fee for sleep data before you click buy.

Buy the Oura Ring 4: Check the Oura Ring 4 →

If you’re ring-curious but not subscription-curious, keep reading the rest of the brand reviews — there are real alternatives.

What to read next

• Best Smart Rings of 2026: The Complete Buyer’s Guide — the full 2026 lineup, ranked.
• Oura Ring 4 vs Ultrahuman Ring PRO — the flagship head-to-head most buyers care about.
• Best Smart Rings with No Subscription — the rings that skip monthly fees entirely.

Frequently Asked Questions

How much does the Oura Ring 4 cost in total?
The ring itself starts around $349 for the standard Silver finish, climbing to $499+ for Gold and Rose Gold finishes. The Oura Membership adds roughly $5.99/month on top — about $72 per year. Year one runs $420 minimum.

What’s the difference between Oura Ring 4 and Gen 3?
Ring 4 is fully titanium inside and out (Gen 3 had a plastic interior with sensor nubs), uses adaptive sensor selection for better accuracy and battery, and has a wider size range from 4–15. Same core measurements, smaller and more comfortable hardware.

Is the Oura Ring 4 waterproof?
Yes for daily wear including showering and swimming. Oura is more cautious about saunas and very high temperature environments. Check the current product page for the specific water resistance rating before activities like deep diving.

What happens if I don’t pay for the Oura Membership?
The ring still records data and the app shows raw heart rate, steps, and basic temperature trends. You lose the Sleep Score, Readiness Score, Activity Score, cycle insights, and most of the daily coaching content. Most reviewers agree the membership is required to get the value.

How long does the Oura Ring 4 battery last?
5 to 8 days per charge, depending on ring size and feature usage. A full charge takes 20–80 minutes. The charger is size-specific.