Galaxy Watch vs Garmin: Which Is More Accurate?
No price, no comfort, no "which should you buy." Just what each device measures, how well-validated that measurement is, and where the two genuinely diverge.
Galaxy Watch and Garmin each appear in the other's top search suggestions, and the independent evidence splits them cleanly. Galaxy Watch has the stronger record for blood oxygen, sleep apnea detection and AFib detection; Garmin has the broader record for heart rate during activity and the only independently tested VO2 max estimate of the two. One study wore both on the same people for calories, and both overestimated. For depth on either, see the full Samsung Galaxy Watch and Garmin profiles.
Which Measures Heart Rate More Accurately?
Samsung Galaxy Watch
The Galaxy Watch Active2 read 3.84 beats per minute high on average against a Holter ECG, better during exercise than at rest.
Garmin
A review of 158 studies named Garmin and Apple Watch the most accurate brands for heart rate, and two current Garmins avoided the larger-error group in a 10-device test.
Where the evidence actually differs
Both have independent heart rate testing; Garmin's is broader, spanning several models, exercise and simulated altitude, while Samsung's current watches have one published exercise test of an older model.
What independent research found
Both tested; Garmin broaderIn 23 healthy adults, the Galaxy Watch Active2 overestimated heart rate by 3.84 beats per minute overall against a Holter ECG, with larger errors at rest and while typing than during exercise (JMIR Formative Research, 2022). Across 158 publications on nine brands, Garmin and Apple Watch were the most accurate for heart rate (JMIR mHealth and uHealth, 2020). In a 10-device comparison against an ECG chest strap, the Garmin Vivosmart 5 and Vivoactive 5 were not among the devices with larger errors (JMIR Formative Research, 2026). At simulated altitude, the Garmin Fenix 5X Plus underestimated resting heart rate by under 1 beat per minute (Research Quarterly for Exercise and Sport, 2021), and the Forerunner 245 gave heart rate data its authors judged acceptable at rest and in exercise at every simulated altitude up to 5,500 metres (International Journal of Sports Medicine, 2021).
Which Measures HRV More Accurately?
Samsung Galaxy Watch
A Samsung Gear Sport, an earlier Samsung watch using the same optical sensing approach, tracked heart rate and HRV closely against an ECG during sleep but not during waking hours.
Garmin
The Garmin Fenix 6 was off by 10.52 percent for overnight HRV against an ECG, the second-weakest of five devices tested.
Where the evidence actually differs
Neither brand's current flagship has an independent HRV test. The two results come from different studies, references and models, so they cannot be ranked against each other.
What independent research found
Older models onlyIn 28 participants monitored for 24 hours against a medical-grade chest ECG, the Samsung Gear Sport's heart rate and time-domain HRV correlated strongly with the reference during sleep, with low bias, while most HRV measures were weaker during waking hours (PLOS One, 2022). In 13 adults over 536 nights against a simultaneous ECG, the Garmin Fenix 6 reached a concordance of 0.87 and an average overnight HRV error of 10.52 percent, behind Oura and Whoop (Physiological Reports, 2025).
Blood Oxygen and Sleep Apnea
Samsung Galaxy Watch
Galaxy Watch 5 met the medical-oximeter accuracy limit in a lab test, Galaxy Watch 4 tracked overnight blood oxygen within about 2.5 percentage points of a sleep lab, and the watch detected moderate-to-severe sleep apnea with 94.1 percent sensitivity.
Garmin
Offers spot-check, all-day and sleep Pulse Ox modes, according to Garmin. Three of four independent tests of Garmin blood oxygen found it unreliable, two of them at altitude.
Where the evidence actually differs
This is the largest gap between the two brands. The four independent tests of Galaxy Watch blood oxygen here found usable accuracy; three of the four tests of Garmin's, across four different models, did not.
What independent research found
Galaxy far aheadGalaxy Watch 5 stayed within the 4 percent limit medical pulse oximeters must meet, against a Masimo clinical oximeter, in 18 young adults breathing reduced-oxygen mixtures (Sensors, 2023). Galaxy Watch 4 overnight blood oxygen showed a root-mean-square error of 2.54 percentage points in 51 adults (Journal of Clinical Sleep Medicine, 2024) and 2.3 percentage points with negligible bias in 97 adults with sleep disturbances (Sleep Health, 2022); Galaxy Watch 6 showed no significant difference from a clinical oximeter, with moderate agreement, in 50 adults aged 50 to 89 at rest (JMIR Formative Research, 2026); and the watch detected moderate-to-severe sleep apnea with 94.1 percent sensitivity and 66.7 percent specificity in 152 adults (Journal of Clinical Sleep Medicine, 2026).
For Garmin, the Venu 2s was the furthest from a clinical oximeter of the smartwatches tested in 49 patients, a mean absolute error of 5.8 percent, reading high on average (PLOS Digital Health, 2023). The Forerunner 245 read higher than the reference, with an overall error rate above 50 percent from sea level to simulated altitude and over 80 percent above 4,800 metres, and its authors concluded it should not be used to assess acclimatisation (International Journal of Sports Medicine, 2021). The Fenix 6 failed the accuracy criterion for blood oxygen under every condition tested, with a concordance of 0.10 (Sensors, 2025). The exception was the Fenix 5X Plus, which overestimated by under 1 percentage point at most simulated altitudes and by 3.3 at 12,000 feet (Research Quarterly for Exercise and Sport, 2021).
Which Tracks Sleep More Accurately?
Samsung Galaxy Watch
Galaxy Watch 3 caught 95.4 percent of sleep and 52.4 percent of wake, and scored four sleep stages at 65.1 percent accuracy, against a sleep lab.
Garmin
Every independent sleep-lab study tested the Vivosmart 4 band. It caught 98 percent of sleep but only 28 percent of wake, with weak stage agreement.
Where the evidence actually differs
No study tested the two together, and Garmin's evidence is all from an entry-level band rather than a current watch. On the separate results, Galaxy Watch was better at noticing time awake.
What independent research found
Both tested separatelyIn 32 healthy adults against in-lab polysomnography, the Galaxy Watch 3 overestimated total sleep by 9.5 minutes, detected 95.4 percent of sleep and 52.4 percent of wake, and classified the four stages with 65.1 percent accuracy, with REM not reliably estimated (Journal of Sleep Medicine, 2023). The Garmin Vivosmart 4 detected 98 percent of sleep but 28 percent of wake, with stage agreement of 0.20 kappa, in 18 adults (PLOS One, 2020), and in a five-device sleep-lab comparison it was the only device that could not estimate total sleep as well as research-grade actigraphy (Sensors, 2024).
How Do the ECG and AFib Features Compare?
Samsung Galaxy Watch
Galaxy Watch 3 detected atrial fibrillation with 85 percent sensitivity and 75 percent specificity in 201 cardiology patients, matching Apple Watch 6.
Garmin
Has an FDA-cleared single-lead ECG app on models including the epix Pro, fenix 7 Pro, Venu 3 and Venu 2 Plus, according to Garmin. No independent accuracy study of it is in the evidence behind this site.
Where the evidence actually differs
Galaxy Watch has a clinical head-to-head result against a 12-lead ECG; Garmin's ECG app has FDA clearance but no published independent accuracy test here.
What independent research found
Galaxy tested, Garmin notIn 201 patients at a cardiology service, the Galaxy Watch 3 matched Apple Watch 6 at 85 percent sensitivity and 75 percent specificity for atrial fibrillation against a physician-read 12-lead ECG, with 17 percent of tracings inconclusive (JACC: Clinical Electrophysiology, 2023).
Calories, Steps and VO2 Max
Samsung Galaxy Watch
Overestimated calories by about 57 on average in a 10-minute test, counted daily steps within 10.5 percent, and has no independent VO2 max test.
Garmin
Overestimated calories by about 69 in the same test. Two Garmins counted treadmill steps within 5 percent, and its VO2 max estimate, built from heart rate against running pace according to Garmin, has been tested on two watches.
Where the evidence actually differs
Calories is the one true head-to-head: both watches were worn by the same 58 people against the same metabolic analyser, and both overestimated, with error growing with body fat.
What independent research found
Tested together on caloriesIn 58 adults doing a 10-minute interval cycling test against indirect calorimetry, the Galaxy Watch 5 overestimated activity calories by an average of 56.76 kcal and the Garmin Forerunner 955 by 68.61 kcal, against 21.60 for Apple Watch Series 8; error rose with body fat percentage for every brand (PLOS One, 2026). For steps, the Garmin Vivoactive 3 and Vivofit 3 were within 5 percent at normal treadmill walking speeds (International Journal of Behavioral Nutrition and Physical Activity, 2022), and the Galaxy Watch 4 within 10.5 percent across a free-living day (Sensors, 2024), different protocols that are not directly comparable. For VO2 max, the Garmin Fenix 6 was within a 7.05 percent average error of a lab test (Sensors, 2025) and the Forerunner 920XT within 7.3 percent (International Journal of Environmental Research and Public Health, 2019).
Common questions
Is Galaxy Watch or Garmin more accurate?
It depends on the measurement. Galaxy Watch has the stronger independent evidence for blood oxygen, sleep apnea detection and AFib detection. Garmin has the broader evidence for heart rate during activity and the only independently tested VO2 max estimate of the two. Worn by the same people, both overestimated calories, Garmin by about 69 and Galaxy by about 57 in a 10-minute test.
Is Garmin blood oxygen accurate?
Mostly not, on the published tests. The Garmin Venu 2s was the furthest from a clinical oximeter of the smartwatches tested in 49 patients, the Forerunner 245 had an error rate above 50 percent at simulated altitude, and the Fenix 6 failed the accuracy criterion. Only the Fenix 5X Plus stayed within about 1 percentage point at most simulated altitudes.
Is Galaxy Watch or Garmin better for sleep tracking?
No study tested them together. Separately, Galaxy Watch 3 caught 52.4 percent of time awake against a sleep lab and scored stages at 65.1 percent accuracy, while the Garmin Vivosmart 4 caught 28 percent of time awake. Every Garmin sleep study tested the Vivosmart band rather than a current Garmin watch.
Are Galaxy Watch calories accurate?
Not precisely. In a 10-minute cycling test the Galaxy Watch 5 overestimated activity calories by about 57 on average, and in longer intermittent running the Galaxy Watch 6 and 7 were within 10 to 13 percent on average. Error rose with body fat percentage across every brand tested.
Does Garmin have an ECG like Galaxy Watch?
Yes. Garmin has an FDA-cleared single-lead ECG app on models including the epix Pro, fenix 7 Pro, Venu 3 and Venu 2 Plus. The Galaxy Watch 3 ECG has been tested independently, detecting AFib with 85 percent sensitivity in cardiology patients; no independent accuracy test of Garmin's ECG app is in the evidence behind this site.
This page won't tell you which to buy. Battery life, GPS, training features and phone compatibility matter to that decision and none of them are evidence questions. What the evidence supports: Galaxy Watch has the stronger blood oxygen, sleep apnea and AFib record; Garmin has the broader heart rate record and tested VO2 max; both overestimate calories. For the full picture on either device, see the complete Samsung Galaxy Watch or Garmin profile.