Device comparisons
Garmin vs Apple Watch: Heart Rate Accuracy from Published Studies
In the studies that tested both brands, Apple Watch agreed more closely with ECG for exercise heart rate and overnight heart rate. Series 10 and Fenix 8 were not the models tested.
Published study results
| Metric | Garmin (Fenix 8 / Forerunner 965) | Apple Watch Series 10 |
|---|---|---|
| Exercise heart rateConcordance vs ECGGillinov et al. 2017, n=50 | 0.81Forerunner 235 | 0.92Apple WatchCloser in this study |
| Overnight heart rateICC vs ECGMiller et al. 2022, n=53 | 0.41Forerunner 245 | 0.96Series 6Closer in this study |
| Sleep stagesEpoch agreement vs PSGMiller et al. 2022, n=53 | 50%κ 0.25 · Forerunner 245 | 53%κ 0.20 · Series 6 |
Each row is one statistic from a study already cited on this page. The link names the sample size when this page already states it. This is not a new measurement.
Devices
Garmin (Fenix 8 / Forerunner 965)
Sports watchDevice guideApple Watch Series 10
SmartwatchDevice guideGarmin fēnix 8 47 mm AMOLED, slate gray case with a black silicone band (part 010-02904-00): product photograph from Garmin. Apple Watch Series 10, jet black aluminum with a black sport band: product photograph from Apple Newsroom, September 2024.
Quick answer
Apple Watch has agreed more closely with ECG in head-to-head studies. During exercise its concordance with ECG was 0.92 versus 0.81 for the Garmin Forerunner 235, and overnight heart rate ICC was 0.96 versus 0.41 for the Forerunner 245. Sleep staging was similar (53% vs 50% agreement with polysomnography). Garmin lasts far longer on a charge.
Sources: Gillinov et al. 2017, Med Sci Sports Exerc; Miller et al. 2022, Sensors
At a glance
Each row is one statistic from one study already cited on this page. Gillinov et al. 2017 measured exercise heart rate in 50 adults. Miller et al. 2022 tested six devices on 53 adults for one night. The tested models are Forerunner 235, Forerunner 245 and Apple Watch Series 6, not Fenix 8 or Series 10.
| Specification | Garmin (Fenix 8 / Forerunner 965) | Apple Watch Series 10 |
|---|---|---|
| Exercise heart rateConcordance vs ECG | 0.81Forerunner 235 | 0.92Apple WatchCloser in this study |
| Overnight heart rateICC vs ECG | 0.41Forerunner 245 | 0.96Series 6Closer in this study |
| Sleep stagesEpoch agreement vs PSGNear tie | 50%κ 0.25 · Forerunner 245 | 53%κ 0.20 · Series 6 |
Primary rows only. The study tables further down list more results from the accuracy database.
Hardware specs
| Specification | Garmin (Fenix 8 / Forerunner 965) | Apple Watch Series 10 |
|---|---|---|
| Battery LifeDiffers | Up to 16 days (Fenix 8 47 mm AMOLED, gesture); up to 23 days (FR965) | Up to 18 hours; up to 36 hours in Low Power Mode |
| Water ResistanceDiffers | 10 ATM + 40 m dive (Fenix 8); 5 ATM (FR965) | 50 m (ISO 22810:2010) |
| ECGDiffers | Fenix 8: ECG app (regional availability) | ECG app; irregular rhythm notifications |
| HRV MetricDiffers | HRV Status: 7-day average vs 3-week baseline | — |
| WeightDiffers | — | 36.4 g (46 mm aluminum, GPS) |
Hardware only. Study results are not repeated in this table. Differs marks values that are not the same. An em dash means this page did not publish that figure.
Specs verified on October 26, 2026: Gillinov et al. 2017, Med Sci Sports Exerc (exercise HR vs ECG, n=50), Miller et al. 2022, Sensors (six devices vs PSG and ECG, n=53), Apple Watch Series 10 technical specifications, FDA De Novo DEN180042: Apple irregular rhythm notification, Garmin Fenix 8 owner's manual: battery information, Garmin Fenix 8 owner's manual: specifications, Garmin Forerunner 965 owner's manual: battery information, Garmin Forerunner 965 owner's manual: specifications, Garmin: ECG App expands to Australia and the EU (Venu 3, Fenix 8), Garmin: Understanding HRV Status.
Pros and cons
Garmin (Fenix 8 / Forerunner 965)
Pros
- Fenix 8 (47 mm AMOLED): up to 16 days smartwatch mode; Forerunner 965: up to 23 days
- HRV Status from overnight HRV against a 3-week baseline
- ECG app on Fenix 8 in eligible regions (30-second recording)
Cons
- Forerunner 235 heart rate concordance with ECG 0.81 vs Apple Watch 0.92 (Gillinov 2017)
- Forerunner 245 overnight heart rate ICC 0.41 vs ECG (Miller 2022)
Apple Watch Series 10
Pros
- ECG app and FDA-authorized irregular rhythm notifications
- Exercise heart rate concordance 0.92 with ECG (Gillinov 2017)
- Overnight heart rate ICC 0.96 vs ECG for Series 6 (Miller 2022)
Cons
- Up to 18 hours normal use (36 hours Low Power Mode)
- Requires an iPhone
- Blood Oxygen is not intended for medical use
What published studies show
One table per metric. These rows come from the accuracy database and are not repeated as a second card list. From the wearable accuracy database (v1.0.0).
Heart rate at rest3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivoactive 4 | ρc = 0.9998Lin's concordance correlation | ECG | n = 263, 30-min standardised recording | Theurl et al. (2023)Independent |
| Apple Watch Series 9 / Ultra 2 | 5.91% (MAE 3.73 bpm)Mean absolute percentage error | Polar H10 + Kubios HRV | n = 39, Serial morning measurements over 14 days, 316 readings | O'Grady et al. (2024)Independent |
| Apple Watch Series 6R-R intervals and BPM at rest | 1.15%Mean absolute percentage error | ECG | n = 78, Lab: rest, talking, movie, before/ | Bonneval et al. (2025)Independent |
Heart rate during exercise9 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 5 | Skin pigmentation did not predict error (P = 0.29)Study finding (no single number) | ECG chest strap (Polar H7/ | n = 28, Rest, cycling, recovery | Mulholland et al. (2026)Independent |
| Garmin Fenix 5 | 2.9%–9.2% (range by intensity)Coefficient of variation | ECG chest strap (Polar H7/ | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Garmin Forerunner 235all exercise conditions | rc = 0.81Lin's concordance correlation | ECG | n = 50, Gillinov: treadmill, bike, elliptical | Gillinov et al. (2017)Funding not reported |
| Apple Watch Series 6 | High agreement in squat, deadlift, cable row (rho > 0.832)Study finding (no single number) | ECG chest strap (Polar H7/ | n = 29, Resistance exercise (5 exercises) | Støve et al. (2022)Funding not reported |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch SE | Significantly lower MAE than Polar Pacer Pro and Galaxy Watch 6Study finding (no single number) | ECG chest strap (Polar H7/ | n = 37, Low/ | Jeong et al. (2026)Independent |
| Apple Watch Series 8 | Skin pigmentation did not predict error (P = 0.62); 50% of missing data from dark-skin participantsStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 28, Rest, cycling, recovery | Mulholland et al. (2026)Independent |
6 more results in the database. Heart rate accuracy across devices →
Overnight heart rate1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 245 Music | ICC 0.41Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Garmin Forerunner 245 Music | 5.4 bpm (absolute bias)Mean absolute error | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Apple Watch Series 6 | ICC 0.96Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Apple Watch Series 6 | 1.5 bpm (absolute bias)Mean absolute error | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
HRV (RMSSD)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Fenix 6 | 10.52%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Garmin Fenix 6 | 0.87Lin's concordance correlation | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| Garmin Forerunner 245 Music | ICC 0.24Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
| Garmin Forerunner 245 Music | 33.1 ms (absolute bias)Mean absolute error (absolute bias) | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivoactive 4 | ρc = 0.66 (moderate)Lin's concordance correlation | ECG | n = 263, 30-min standardised recording | Theurl et al. (2023)Independent |
| Apple Watch Series 9 / Ultra 2 | 28.88% (MAE 20.46 ms)Mean absolute percentage error | Polar H10 + Kubios HRV | n = 39, Serial morning measurements over 14 days, 316 readings | O'Grady et al. (2024)Independent |
2 more results in the database. HRV accuracy across devices →
Sleep stages (4-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 245 Music | 50%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Garmin Forerunner 245 Music | κ = 0.25Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Garmin Vivosmart 4 | κ = 0.21Cohen's kappa | Polysomnography (PSG) | n = 25, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Apple Watch Series 8 | κ = 0.53Cohen's kappa | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 8 | 50.5–86.1% (range across stages)Sensitivity | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
| Apple Watch Series 8deep sleep duration | Deep sleep −43 minMean bias (signed) | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
4 more results in the database. Sleep accuracy across devices →
Sleep vs wake (2-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 4 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Garmin Fenix 5S | Worse than actigraphyStudy finding (no single number) | Polysomnography (PSG) | n = 34, Sleep laboratory, 3 nights incl. disrupted night | Chinoy et al. (2021)Funding not reported |
| Garmin Vivosmart 3 | Worse than actigraphyStudy finding (no single number) | Polysomnography (PSG) | n = 34, Sleep laboratory, 3 nights incl. disrupted night | Chinoy et al. (2021)Funding not reported |
| Garmin Forerunner 245 Music | 89%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 245 Music | κ = 0.35Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Other maker funded |
| Apple Watch Series 8 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
3 more results in the database. Sleep accuracy across devices →
Total sleep time1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 945 | MAE 84.63 min (overestimate)Mean absolute error | Polysomnography (PSG) | n = 49, 1 night PSG + MSLT | Budig et al. (2022)Independent |
Blood oxygen (SpO2)11 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Vivosmart 4 | 3.3% (rest)Root-mean-square error | Medical-grade pulse oximeter | n = 36, Rest, COPD outpatients | Støve et al. (2023)Funding not reported |
| Garmin Venu 2S | 5.8% (RMSE 6.7%)Mean absolute error | Medical-grade pulse oximeter | n = 49, Spot readings, with and without chronic pulmonary disease | Jiang et al. (2023)Independent |
| Garmin Venu 2S | 6.7%Root-mean-square error | Medical-grade pulse oximeter | n = 49, Spot readings, with and without chronic pulmonary disease | Jiang et al. (2023)Independent |
| Garmin Fenix 5X Plus | 9.77% (ICC 0.549)Mean absolute percentage error | Arterial blood gas (SaO2) | n = 13, High altitude 4559 m | Schiefer et al. (2021)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Fenix 5X Plus | +3.3% at 12,000 ft (LoA −1.9 to 8.6%)Mean bias (signed) | Medical-grade pulse oximeter | n = 23, Normobaric hypoxia, rest, 900–12,000 ft | Lauterbach et al. (2021)Funding not reported |
| Garmin Fenix 6 | 4.29% (CCC 0.10)Mean absolute percentage error | Medical-grade pulse oximeter | n = 22, Normoxic and hypoxic conditions | Carrier et al. (2025)Independent |
10 more results in the database. SpO2 accuracy across devices →
Atrial fibrillation detection4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 6smartwatch ECG app, inconclusive tracings counted | 85% (spec 75%)Sensitivity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Apple Watch Series 6smartwatch ECG app, inconclusive tracings counted | 75%Specificity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Apple Watch + KardiaBand (SmartRhythm 2.0)AF episodes ≥ 1 h | 97.5% episode sensitivity (PPV 39.9%)Sensitivity | Insertable cardiac monitor | n = 24, Ambulatory, 31,348.9 h of recordings | Wasserlauf et al. (2019)Funding not reported |
| Apple Watch (irregular rhythm notification)PPG irregular pulse notification | PPV 0.84 (95% CI 0.76–0.92)Positive predictive value | ECG patch | n = 419297, Siteless pragmatic study; ECG patch after notification | Perez et al. (2019)Maker funded |
More results (1)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Kardia Band on Apple Watch (single-lead ECG)automated ECG read; 57 of 169 recordings non-interpretable | Sens 93% / spec 84% (interpretable recordings)Sensitivity | 12-lead ECG | n = 100, Before and after cardioversion | Bumgarner et al. (2018)Funding not reported |
VO2max estimate6 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Forerunner 245 | 7.9% / 7.2% (two runs)Mean absolute percentage error | Indirect calorimetry | n = 35, Treadmill ramp test | Engel et al. (2026)Funding not reported |
| Garmin Fenix 6 | 7.05% (CCC 0.73)Mean absolute percentage error | Indirect calorimetry | n = 19, Graded exercise test and outdoor run | Carrier et al. (2025)Independent |
| Garmin Forerunner 920XT | 7.3%Mean absolute percentage error | Indirect calorimetry | n = 24, Lab | Passler et al. (2019)Independent |
| Apple Watch Series 10 | 13.2% (MAE 6.79 mL/kg/min)Mean absolute percentage error | Indirect calorimetry | n = 40, Maximal treadmill test (modified Åstrand) | Lambe et al. (2026)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch | 13.31% (MAE 6.92 mL/kg/min)Mean absolute percentage error | Indirect calorimetry | n = 30, Maximal treadmill test (modified Åstrand) | Lambe et al. (2025)Independent |
| Apple Watch Series 7 | 15.79% (ICC 0.47)Mean absolute percentage error | Indirect calorimetry | n = 19, Graded cycle ergometer test | Caserman et al. (2024)Independent |
Energy expenditure (calories)6 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Garmin Fenix 5 | 15.9%–34.5% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Garmin Forerunner 955physical activity energy expenditure, 10 min | +68.61 kcalMean bias (signed) | Indirect calorimetry | n = 51, 10-min recumbent cycling intervals | Kostrna et al. (2026)Independent |
| Garmin Fenix 6walking | 32.0% walk / 21.8% runMean absolute percentage error | Indirect calorimetry | n = 20, Outdoor 2-km walk (6 km/ | Le et al. (2022)Independent |
| Apple Watch Series 9 | Inconsistent across all groupsStudy finding (no single number) | Indirect calorimetry | n = 30, 10-min treadmill | Chase et al. (2024)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Apple Watch Series 4 | 13.5%–27.1% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Apple Watch Series 6 | 14.68–24.85% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
3 more results in the database. Calories accuracy across devices →
Verdict
Pick Apple Watch if you use an iPhone and want ECG, irregular rhythm notifications and the closer ECG agreement Apple Watch showed in independent studies. Pick Garmin if battery measured in weeks and training features matter more. The studies used older models (Forerunner 235/245, Apple Watch Series 6), so treat them as brand-level evidence.
Frequently asked questions
Is Apple Watch or Garmin better for heart monitoring?
In Gillinov et al. (2017), Apple Watch agreed more closely with ECG during exercise (concordance 0.92) than the Garmin Forerunner 235 (0.81). Apple Watch also has an ECG app and irregular rhythm notifications; Garmin offers its ECG app on select models such as Fenix 8 and Venu 3.
Which is more accurate for sleep, Garmin or Apple Watch?
In a 53-adult polysomnography study (Miller et al., 2022), sleep-stage agreement was 53% (κ 0.20) for Apple Watch S6 and 50% (κ 0.25) for Garmin Forerunner 245. Both were valid for sleep timing but weak at staging.
Which has better overnight heart rate and HRV accuracy?
In Miller et al. (2022), Apple Watch S6 overnight heart rate agreed with ECG at ICC 0.96 versus 0.41 for the Forerunner 245. HRV ICC was 0.67 for Apple Watch; Garmin's 0.24 came from a 3-minute manual test while awake, so it is not a like-for-like comparison.
Which has longer battery life?
Garmin states up to 16 days for the Fenix 8 47 mm AMOLED (gesture display) and up to 23 days for the Forerunner 965 in smartwatch mode. Apple states up to 18 hours for Series 10, or 36 hours in Low Power Mode.
Device research records
Datasets, papers and validation results for the models named on this page.