For tracking HRV, the Oura Ring is the best-documented smart ring: Oura says how its nightly number is built, and independent studies have tested it overnight against an ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG or a chest strap. It is also the only ring of the four here that needs a membership to show that number, so the choice comes down to how much the evidence and the export are worth to you against the price.
Documentation checked: 24 October 2026. Ring makers change their apps, prices and algorithms often.
This guide compares the four on HRV alone: what each ring reports, how well it has been tested, what it costs and where the data can go. It does not rank sleep staging, step counts or design. For each ring in depth, see Oura, Galaxy Ring, Ultrahuman and RingConn.
Four rings, five questions for HRV
Makers’ pages and studies, 24 October 2026
| Oura Ring | Galaxy Ring | Ultrahuman Ring | RingConn | |
|---|---|---|---|---|
| Names its HRV statistic | In part: Not on Oura’s help page; study authors report RMSSD | No: Formula not published | Yes: RMSSD, in Ultrahuman’s own paper | Yes: RMSSD, RingConn says |
| Publishes when it measures | Yes: Mean of 5-minute samples through the night’s sleep | No: During sleep; which part of the night is not published | Yes: About 24 s every 5 to 6 minutes in sleep, averaged | No: Around the clock; the nightly window is not published |
| Peer-reviewed test against an ECG or chest strap | Yes: Several independent overnight studies, the latest on the Ring 4 | No: None found | No: Only Ultrahuman’s own nine-night comparison, not peer reviewed | In part: One study, seated athletes, with RingConn’s firmware and staff |
| Nightly HRV without a subscription | No: Membership needed; without it, three daily scores only | Yes: No subscription; needs an Android phone | Yes: No subscription for ring data | Yes: No subscription |
| HRV can leave the app | Yes: CSV export without a membership; Health Connect with one | Not stated: Download personal data; Samsung does not list the files | In part: To Apple Health, and a personal API token; no file export documented | No: Not to Health Connect or Apple Health; a copy only by request |
A table of four smart rings, Oura Ring, Galaxy Ring, Ultrahuman Ring and RingConn, against five questions. Each answer starts with its mark in words. Names its HRV statistic Oura Ring: In part, Not on Oura’s help page; study authors report RMSSD. Galaxy Ring: No, Formula not published. Ultrahuman Ring: Yes, RMSSD, in Ultrahuman’s own paper. RingConn: Yes, RMSSD, RingConn says. Publishes when it measures Oura Ring: Yes, Mean of 5-minute samples through the night’s sleep. Galaxy Ring: No, During sleep; which part of the night is not published. Ultrahuman Ring: Yes, About 24 s every 5 to 6 minutes in sleep, averaged. RingConn: No, Around the clock; the nightly window is not published. Peer-reviewed test against an ECG or chest strap Oura Ring: Yes, Several independent overnight studies, the latest on the Ring 4. Galaxy Ring: No, None found. Ultrahuman Ring: No, Only Ultrahuman’s own nine-night comparison, not peer reviewed. RingConn: In part, One study, seated athletes, with RingConn’s firmware and staff. Nightly HRV without a subscription Oura Ring: No, Membership needed; without it, three daily scores only. Galaxy Ring: Yes, No subscription; needs an Android phone. Ultrahuman Ring: Yes, No subscription for ring data. RingConn: Yes, No subscription. HRV can leave the app Oura Ring: Yes, CSV export without a membership; Health Connect with one. Galaxy Ring: Not stated, Download personal data; Samsung does not list the files. Ultrahuman Ring: In part, To Apple Health, and a personal API token; no file export documented. RingConn: No, Not to Health Connect or Apple Health; a copy only by request.
What each ring reports as HRV
All four read your pulse with light at the finger and take the beat-to-beat timing from it. They differ in which statistic they report and which part of the day or night it covers.
| Statistic | When | Daily score built on it | |
|---|---|---|---|
| Oura Ring | RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD , as the study authors report it | During sleep: the mean of 5-minute samples, plus the night’s maximum | Readiness, through HRV Balance |
| Galaxy Ring | Not published | During sleep; the window is not published | Energy Score |
| Ultrahuman Ring | RMSSD | About 24 seconds every 5 to 6 minutes during sleep, averaged | Dynamic Recovery, through HRV Form |
| RingConn | RMSSD, RingConn says | Around the clock; the nightly window is not published | Stress Index Baevsky stress index A number built from the histogram of heartbeat intervals, with no unit. It rises as the rhythm gets steadier and less variable, which Baevsky read as strain on the body's regulation. More about Baevsky stress index |
From each maker’s pages (see Sources), read on 24 October 2026.
Oura measures HRV only during sleep, apart from snapshots in some guided sessions. It takes 5-minute samples through the night, and “the average HRV value you see is the mean of all five-minute samples taken while you sleep”, shown next to the night’s highest sample (Oura Member Care, HRV). Oura’s help page does not name the statistic; the authors of the 2025 Dial study report that Oura’s nightly value is RMSSD.
Ultrahuman defines its nightly number, Sleep HRV, as “the mean RMSSD of readings retained during sleep”. The ring records about 24 seconds of beat intervals every 5 to 6 minutes, and a quality check drops readings with too few good beats (Ultrahuman Science, 2026). In September 2026 Ultrahuman changed the algorithm, and in its own analysis members’ median Sleep HRV fell from 69 to 46 ms; Ultrahuman HRV explains why to compare nights after the change only with each other.
RingConn says its “HRV terminology uses RMSSD” (RingConn, health scores), and its comparison page lists HRV as “24/7 Monitoring” on all three rings (RingConn, compare). It does not say which part of the night a nightly value covers.
Samsung calls the Galaxy Ring’s measure heart rate variability, or “Sleeping Heart Rate Variability” in the Energy Score (Samsung Newsroom, 2024), and publishes neither the statistic nor the window.
RMSSD, the root mean square of successive differences between beats, is a standard time-domain measure of beat-to-beat variation (Task Force, 1996). Two rings that both report RMSSD still rarely show the same number, because each averages its own stretch of the night and cleans the signal its own way. Compare each ring only with itself; why Oura and WHOOP show different HRV explains the effect of the window.
Which smart ring is most accurate for HRV?
Oura’s rings are the only ones with independent, peer-reviewed tests of the nightly HRV against an ECG or a chest strap. For the other three the evidence is thin or missing. That leaves them untested; it does not show that they are inaccurate.
Oura: several overnight studies
The largest is a 2025 home study by Dial and colleagues: 13 healthy adults wore several devices and a Polar H10 chest strap, the reference, for 536 nights in total. The authors declare no competing interests. For overnight RMSSD:
| Nights | Concordance (CCC) | Average error (MAPE) | Average error in ms | |
|---|---|---|---|---|
| Oura Ring 4 (Gen 4) | 139 | 0.99 | 5.96% | 3.93 |
| Oura Ring Gen 3 | 470 | 0.97 | 7.15% | 3.91 |
Overnight RMSSD against a Polar H10 (Dial and colleagues, 2025). A concordance of 1 means perfect agreement.
At an RMSSD of 50 ms, an average error of about 6% is about 3 ms. Other studies of Oura’s rings found more mixed results:
- At home against a chest ECG, 35 adults: the ring’s nightly RMSSD tracked the ECG closely (r = 0.96) but read 15.88 ms low on average (Cao and colleagues, 2022).
- One night in a sleep laboratory, 53 adults: the Gen 2 app value read 10.2 ms low on average, with an intraclass correlation of 0.63 (Miller and colleagues, 2022).
- Against a medical ECG, 49 people aged 15 to 72: nightly HRV agreed with r² = 0.980 and a bias of −1.2 ms (Kinnunen and colleagues, 2020). The first author works for Oura.
- From the Gen 3’s beat data, researchers in Singapore got accurate RMSSD when they kept 5-minute segments with about 80% valid beats and averaged over at least 30 minutes (Liang and colleagues, 2024).
The Oura Ring 5, which Oura now sells next to the Ring 4, has not been tested.
RingConn: one study, at rest
Tao and colleagues recorded 64 shooting and archery athletes for 10 minutes while they sat still after training, wearing a RingConn Gen 2 and a Polar H10. The researchers took the ring’s raw light signal through research firmware and worked out RMSSD themselves. It read 3.237 ms higher than the strap on average, with 95% limits of agreement from −8.591 to +15.065 ms (Tao and colleagues, 2026). RingConn supplied the rings and firmware, and three of the seven authors work for RingConn or the company that helped develop the ring. The study did not test sleep or the number the app shows.
Ultrahuman and Galaxy Ring: no peer-reviewed study
A search of PubMed, Europe PMC and Crossref on 24 October 2026 found no peer-reviewed study comparing either ring’s HRV with an ECG or a chest strap. Ultrahuman has published its own comparison: nine adults, one night each against an ECG chest strap, written by four Ultrahuman staff and posted on its website (Ultrahuman Science, 2026). It reports close agreement for the nightly value, but it is not a peer-reviewed paper. Samsung has published nothing on the Galaxy Ring’s HRV accuracy.
Peer-reviewed HRV studies of rings and Samsung wearables in our tracker
Validation tracker
Year the study was published
We searched PubMed, Europe PMC and Crossref for a Galaxy Ring HRV study on 22 October 2026 and found none. The Gear Sport is an older Samsung watch, and its researchers analysed the watch’s pulse signal themselves rather than a number from the app.
Sources: Kinnunen and colleagues, 2020, Stone and colleagues, 2021, Miller and colleagues, 2022, Cao and colleagues, 2022, Sarhaddi and colleagues, 2022, Dial and colleagues, 2025, Tao and colleagues, 2026. Every study with its numbers is in the device validation tracker.
A timeline from 2020 to 2026 with one row per device, from the device validation tracker. Oura Ring Gen 4: Dial and colleagues, 2025, 13 people, asleep. Oura Ring Gen 3: Dial and colleagues, 2025, 13 people, asleep. Oura Ring Gen 2: Stone and colleagues, 2021, 5 people, at rest and Miller and colleagues, 2022, 53 people, asleep. Oura Ring: Kinnunen and colleagues, 2020, 49 people, asleep and Cao and colleagues, 2022, 35 people, asleep. RingConn Gen 2: Tao and colleagues, 2026, 64 people, at rest. Samsung Gear Sport: Sarhaddi and colleagues, 2022, 28 people, asleep and through the day. Samsung Galaxy Ring: no study, from going on sale in July 2024 to our search in October 2026. We searched PubMed, Europe PMC and Crossref for a Galaxy Ring HRV study on 22 October 2026 and found none. The Gear Sport is an older Samsung watch, and its researchers analysed the watch’s pulse signal themselves rather than a number from the app.
The chart shows the peer-reviewed studies in our device validation tracker. Ultrahuman has no row because it has no peer-reviewed study. A dot means a study exists, not that the ring did well.
Daily scores: what each ring builds on HRV
Each app turns HRV into a daily score, and in each the HRV is one input among several, with weights the maker does not publish.
What is in a readiness score?
From the makers' own documentation
- HRV : named by the maker HRV Balance: "How has my HRV changed over the past few weeks?" (a two-week average against three months).
- Resting heart rate : named by the maker Resting Heart Rate: "Was my RHR substantially higher or lower than usual?"
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep, Sleep Balance, Sleep Regularity and Recovery Index (hours of sleep after the heart rate reached its low).
- Temperature : named by the maker Body Temperature: "Is my body temperature higher or substantially lower than usual?"
- Activity or load : named by the maker Previous Day Activity and Activity Balance (recent load).
Oura's Readiness Score names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. "The sum of these daily Readiness Contributors make up your Readiness Score." No weights are published.
- HRV : named by the maker Heart rate variability.
- Resting heart rate : named by the maker Sleeping heart rate.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep time average, sleep time consistency, bed and wake time consistency, and sleep timing.
- Temperature : not named Not named by the maker.
- Activity or load : named by the maker Previous day activity.
Samsung's Energy Score names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Samsung lists the metrics the score combines and nothing about their weights.
- HRV : named by the maker HRV Form: your HRV baseline and how far last night departs from it; also the Stress Rhythm Score, which tracks heart rate and HRV across the day.
- Resting heart rate : named by the maker Overnight resting heart rate against your own baseline.
- Breathing rate : not named Not named by the maker.
- Sleep : named by the maker Sleep Index: length, efficiency, stage split and timing.
- Temperature : named by the maker Skin temperature against your usual overnight level.
- Activity or load : not named Not named by the maker.
Ultrahuman's Recovery Score names 4 of the six inputs: HRV, resting heart rate, sleep and temperature. "Each is graded on its own; then the five combine into the 0 to 100 score." No weights are published.
Source: Recovery Score (Ultrahuman)
- HRV : named by the maker Heart rate variability from the ring’s optical sensor: "A Stress Index of 50 is not an HRV of 50 milliseconds."
- Resting heart rate : not named Not named by the maker.
- Breathing rate : not named Not named by the maker.
- Sleep : not named Not named by the maker.
- Temperature : not named Not named by the maker.
- Activity or load : not named Not named by the maker.
Also: Heart rate at the time: the software "uses heart-rate and beat-interval information to estimate a stress index". Resting heart rate is not named.
RingConn's Stress Index names 1 of the six inputs, HRV, and others beyond them. RingConn publishes the four bands and calls them "RingConn-specific". It gives no formula.
Source: RingConn Stress Index: scores, HRV and daily patterns (RingConn)
A list of scores, one per device, with six inputs for each: HRV, resting heart rate, breathing rate, sleep, temperature and activity or load. Oura's Readiness Score names 5 of the six inputs: HRV, resting heart rate, sleep, temperature and activity or load. "The sum of these daily Readiness Contributors make up your Readiness Score." No weights are published. Samsung's Energy Score names 4 of the six inputs: HRV, resting heart rate, sleep and activity or load. Samsung lists the metrics the score combines and nothing about their weights. Ultrahuman's Recovery Score names 4 of the six inputs: HRV, resting heart rate, sleep and temperature. "Each is graded on its own; then the five combine into the 0 to 100 score." No weights are published. RingConn's Stress Index names 1 of the six inputs, HRV, and others beyond them. RingConn publishes the four bands and calls them "RingConn-specific". It gives no formula.
A Readiness of 70 and an Energy Score of 70 are not the same thing. If you track HRV, read the nightly HRV behind the score; recovery scores explained lists each score’s inputs.
Cost over three years
On 24 October 2026, the makers’ US pages gave these starting prices. Only Oura charges a subscription to show the nightly HRV.
| Ring | Ring price (US) | Subscription for nightly HRV | 3 years |
|---|---|---|---|
| RingConn Gen 2 Air | $199 | None | $199 |
| RingConn Gen 2 | $299 | None | $299 |
| Galaxy Ring | $399.99 (offered from $299.99) | None | $299.99 to $399.99 |
| RingConn Gen 3 | $349 | None | $349 |
| Ultrahuman Ring AIR | $349 | None | $349 |
| Ultrahuman Ring PRO | $479 | None | $479 |
| Oura Ring | Not read (see below) | $69.99 a year | Ring + $209.97 |
Starting prices from each maker’s US page (see Sources); some sizes and finishes cost more. Samsung’s buy page listed every size and finish at $399.99, the launch price (Samsung Newsroom, 2024), while its Galaxy Ring page said “From $299.99 before trade-in”, an offer that may not last. Ultrahuman’s AIR price is from the comparison table on its US Ring PRO page.
Oura’s store showed us its prices in another currency, so the ring’s US price is not in the table. Oura’s membership costs $5.99 a month or $69.99 a year in the US, after one included month with a new ring (Oura Member Care, membership), so three years add 3 × $69.99 = $209.97 to whatever the ring costs. Ultrahuman sells an optional plan, Ultrahuman Max, from $9.99 a month, but says “there are no recurring subscription fees for accessing your data” (Ultrahuman, US store; Ultrahuman, FAQ). Samsung Health’s paid content is optional iFIT workouts (Samsung Health, US). Cheapest HRV tracking compares rings with straps, watches and bands.
Getting your HRV out of the app
Where your HRV history can go, into a spreadsheet or another app, depends on the ring.
- Oura: a CSV export from the Membership Hub, “even without a membership” (Oura Member Care, membership). With a membership, the Oura API’s sleep data holds the night’s average HRV and the samples behind it (Oura API), and HRV goes to Android’s Health Connect (Oura Member Care, Health Connect). Oura’s Apple Health list does not include HRV (Oura Member Care, Apple Health).
- Ultrahuman: HRV syncs to Apple Health (Ultrahuman Blog). For programmers, Ultrahuman’s developer documentation offers a personal API token that reads your own daily metrics, HRV included, up to 7 days per request (Ultrahuman, UltraSignal API). We found no Ultrahuman page that documents a file export of ring data or HRV in Health Connect.
- Galaxy Ring: Samsung Health’s “Download personal data” saves files to your phone, but Samsung does not list what they hold (Samsung Support). Samsung’s list of data it syncs to Health Connect names activity, heart rate and sleep, not HRV (Samsung Developer).
- RingConn: HRV does not sync to Health Connect, which RingConn blames on “an algorithm compatibility issue” (RingConn, Health Connect), and it is not on RingConn’s Apple Health list (RingConn Support, Gen 3). Your HRV history stays in RingConn’s app.
None of the four documents an export of beat-to-beat intervals. Export your HRV data explains what each depth of export lets you do.
What happens when you stop paying
Only Oura has anything to stop. Without a membership the app shows only the three daily scores, Readiness, Activity and Sleep, but Oura says your data “will remain securely saved”, the CSV export still works, and your history comes back “immediately” if you rejoin (Oura Member Care, membership). The API stops. What happens to my Oura data if I cancel has the steps, and the wearable data rights guide covers what each company keeps and how to ask for a copy.
Battery and fit
Battery life matters for HRV because a night without the ring is a night without a value. The makers’ own figures:
- Oura Ring 5: 6 to 9 days, “depending on ring size and usage” (Oura, Ring 5).
- Galaxy Ring: up to 7 days for sizes 12 and 13 and up to 6 days for smaller sizes, or up to 14 days with the charging case (Samsung, Galaxy Ring).
- Ultrahuman: 4 to 6 days for the Ring AIR (Ultrahuman, FAQ); up to 15 days for the Ring PRO (Ultrahuman, US store).
- RingConn: up to 10 days for the Gen 2 Air, 10 to 12 days for the Gen 2, and up to 14 days for the Gen 3 with vibration off (RingConn product pages).
Charge each ring while you are awake. Whichever you choose, keep it on the same finger every night: a move to another finger, a new ring or an algorithm update can shift the numbers, so start a new series after any of them (can a software update change my HRV).
Other smart rings
- Amazfit Helio Ring. Amazfit’s help page says the ring gives a readiness score Readiness score A single number, often out of 100, that a device builds from your HRV, resting heart rate, sleep and other inputs to suggest how ready you are for the day. The weighting is not published. More about Readiness score at the end of the night’s sleep (Amazfit Support), but it does not describe the HRV, and Amazfit’s US store did not list the ring on 24 October 2026. Amazfit HRV covers the brand’s watches and straps.
- Circular Ring 2. Circular says it computes RMSSD “during the most stable portion of sleep” and publishes agreement figures against an ECG on its own website, without naming a paper (Circular, science). We found no peer-reviewed study of its HRV.
Which smart ring should you choose for HRV?
- For the most evidence and the most detail, choose Oura. It is the only ring with independent overnight validation, it publishes its window, its HRV can leave the app as a CSV file, and its API carries the samples behind each night. Budget for the membership; without it you lose the nightly number.
- For no subscription and a published method, choose Ultrahuman. Its Sleep HRV is defined in detail and syncs to Apple Health. Until a peer-reviewed study appears, read it as a trend, and keep nights before and after the September 2026 algorithm change apart.
- For the lowest price, choose a RingConn. The Gen 2 Air is $199 with no subscription. RingConn’s one study tested the Gen 2 in seated athletes, RingConn does not publish its nightly window, and the HRV cannot leave its app.
- If you live in Samsung Health, choose the Galaxy Ring. It needs no subscription and feeds the Energy Score, but it needs an Android phone, and Samsung publishes no formula, window or validation, so read its HRV only against your own past nights.
A ring is not the only way to track HRV. A chest strap reads the heart’s electrical signal and was the reference in the Dial study; the chest-strap guide explains how, and overnight vs morning HRV explains why a morning reading and a ring’s night are two different series. WHOOP vs Oura compares the leading ring with a band, and HRV by device covers every brand.
When to talk to a doctor
None of these rings diagnoses anything, and none of their scores is a medical test. Talk to a doctor if low HRV or a run of low scores comes with feeling unwell, lasting fatigue, palpitations, dizziness, fainting or chest pain, whatever the number says.