Device comparisons
Fitbit vs Garmin: Heart Rate Accuracy from Published Studies
Older-model studies give mixed results. During exercise, the Garmin Forerunner 235 agreed more closely with ECG than the Fitbit Blaze (concordance 0.81 vs 0.67; Gillinov 2017). For sleep, Fitbit Alta HR performed as well as or better than actigraphy while Garmin Fenix 5S and Vivosmart 3 did worse (Chinoy 2021), and Fitbit Sense and Charge 5 (κ 0.42/0.41) beat Garmin Vivosmart 4 (κ 0.21) in Schyvens 2025.
Published study results
| Metric | Fitbit (Charge 6 / Sense 2) | Garmin (Venu 3 / Forerunner 265) |
|---|---|---|
| Exercise heart rateConcordance vs ECGGillinov et al. 2017, n=50 | 0.67Fitbit Blaze | 0.81Forerunner 235Closer in this study |
| Sleep stagesCohen's κ vs polysomnographySchyvens et al. 2025, n=62 | 0.42 / 0.41Sense / Charge 5Closer in this study | 0.21Vivosmart 4 |
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
Fitbit (Charge 6 / Sense 2)
TrackerDevice guideGarmin (Venu 3 / Forerunner 265)
Sports watchDevice guideFitbit Charge 6 with a coral band: product photograph from the Google Store. Garmin fēnix 8 47 mm AMOLED, slate gray case with a black silicone band (part 010-02904-00): product photograph from Garmin.
At a glance
Each row is one statistic from one study of older models. Gillinov et al. 2017 tested exercise heart rate in 50 adults. Schyvens et al. 2025 tested sleep staging in 62 adults. Current Charge 6, Sense 2 and Forerunner 265 models were not those devices.
| Specification | Fitbit (Charge 6 / Sense 2) | Garmin (Venu 3 / Forerunner 265) |
|---|---|---|
| Exercise heart rateConcordance vs ECG | 0.67Fitbit Blaze | 0.81Forerunner 235Closer in this study |
| Sleep stagesCohen's κ vs polysomnography | 0.42 / 0.41Sense / Charge 5Closer in this study | 0.21Vivosmart 4 |
Primary rows only. The study tables further down list more results from the accuracy database.
Hardware specs
| Specification | Fitbit (Charge 6 / Sense 2) | Garmin (Venu 3 / Forerunner 265) |
|---|---|---|
| Battery LifeDiffers | Up to 7 days (Charge 6); 6+ days (Sense 2) | Up to 14 days (Venu 3); 13 days (FR265) |
| Water ResistanceDiffers | 50 m | 5 ATM |
| ECGDiffers | ECG app | Venu 3: ECG App |
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 17, 2026: Gillinov et al. 2017, Med Sci Sports Exerc (exercise HR vs ECG, n=50), Chinoy et al. 2021, Sleep (seven sleep trackers vs PSG), Schyvens et al. 2025, Sleep Advances (six devices vs PSG, n=62), Lubitz et al. 2022, Circulation (Fitbit Heart Study), Google Store: Fitbit Charge 6 tech specs, Google Store: Fitbit Sense 2 tech specs, Garmin Venu 3 owner's manual: battery information, Garmin Forerunner 265 owner's manual: battery information, Garmin Forerunner 265 owner's manual: specifications, Garmin: ECG App expands to Australia and the EU (Venu 3, Fenix 8).
Pros and cons
Fitbit (Charge 6 / Sense 2)
Pros
- Sleep-stage κ 0.42 (Sense) and 0.41 (Charge 5) vs 0.21 for Vivosmart 4 (Schyvens 2025)
- ECG app
- Fitbit Heart Study: 98.2% PPV for concurrent AF
Cons
- Fitbit Blaze exercise HR concordance 0.67 vs ECG (Gillinov 2017)
- Up to 7 days battery (Charge 6), 6+ days (Sense 2)
Garmin (Venu 3 / Forerunner 265)
Pros
- Forerunner 235 exercise HR concordance 0.81 vs ECG (Gillinov 2017)
- Up to 14 days (Venu 3), 13 days (FR265)
- Venu 3: ECG App (regional availability)
Cons
- Vivosmart 4 sleep-stage κ 0.21 (Schyvens 2025)
- Fenix 5S / Vivosmart 3 worse than actigraphy for sleep/wake (Chinoy 2021)
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 |
|---|---|---|---|---|
| Fitbit Charge 4 | 7.8 bpm (seated rest)Mean absolute error | Holter ECG | n = 23, Rest, sedentary, low- and high-intensity phases | Nissen et al. (2022)Independent |
| Fitbit Charge 4 | ICC 0.80 (COPD) / 0.79 (controls)Intraclass correlation | ECG chest strap (Polar H7/ | n = 55, 5 days free-living | Hermans et al. (2024)Funding not reported |
| Garmin Vivoactive 4 | ρc = 0.9998Lin's concordance correlation | ECG | n = 263, 30-min standardised recording | Theurl et al. (2023)Independent |
Heart rate during exercise6 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Charge 6mixed rest/stress/walking | 4.5 bpmMean absolute error | ECG chest strap (Zephyr BioHarness / | n = 45, Rest, cognitive stress, steady and intermittent walking in neutral/ | Gielen et al. (2026)Funding not reported |
| Fitbit Inspire 3mixed rest/stress/walking | 9–14 bpm (group range)Mean absolute error | ECG chest strap (Zephyr BioHarness / | n = 45, Rest, cognitive stress, steady and intermittent walking in neutral/ | Gielen et al. (2026)Funding not reported |
| Fitbit Charge 4squats | 15.7 bpm (squats)Mean absolute error | Holter ECG | n = 23, Rest, sedentary, low- and high-intensity phases | Nissen et al. (2022)Independent |
| Fitbit Versa | 4.1%–19.1% (range by intensity)Coefficient of variation | ECG chest strap (Polar H7/ | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Sense | 4.14–10.76%Coefficient of variation | ECG chest strap (Polar H7/ | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Fitbit Blazeall exercise conditions | rc = 0.67Lin's concordance correlation | ECG | n = 50, Gillinov: treadmill, bike, elliptical | Gillinov et al. (2017)Funding not reported |
3 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 |
HRV (RMSSD)3 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 (1)
| 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 |
Sleep stages (4-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Sense | κ = 0.42Cohen's kappa | Polysomnography (PSG) | n = 37, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Fitbit Charge 5 | κ = 0.41Cohen's kappa | Polysomnography (PSG) | n = 39, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Fitbit Sense 2 | 61.7–78.0% (range across stages)Sensitivity | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
| Fitbit Sense 2deep sleep duration | Deep sleep −15 minMean bias (signed) | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Sense 2 | κ = 0.42Cohen's kappa | Polysomnography (PSG) | n = 26, Two Korean sleep centres, in-lab PSG | Lee et al. (2023)Independent |
| Fitbit Sense 2 | 64.6%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 26, Two Korean sleep centres, in-lab PSG | Lee et al. (2023)Independent |
3 more results in the database. Sleep accuracy across devices →
Sleep vs wake (2-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Charge 5 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Fitbit Sense | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| Fitbit Sense 2 | ≥ 95%Sensitivity | Polysomnography (PSG) | n = 35, Inpatient, 1 night | Robbins et al. (2024)Other maker funded |
| Fitbit Alta HR | As good as or better than actigraphyStudy finding (no single number) | Polysomnography (PSG) | n = 34, Sleep laboratory, 3 nights incl. disrupted night | Chinoy et al. (2021)Funding not reported |
More results (2)
| 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 |
3 more results in the database. Sleep accuracy across devices →
Total sleep time2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Sense 2 | −74.5 min (older adults)Mean bias (signed) | Polysomnography (PSG) | n = 19, 1 night | Searles et al. (2026)Funding not reported |
| 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)6 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Charge 4 | ICC 0.32 (COPD, overnight)Intraclass correlation | Medical-grade pulse oximeter | n = 30, 4 nights | Hermans et al. (2024)Funding not reported |
| 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 |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 |
| 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 |
1 more result in the database. SpO2 accuracy across devices →
Atrial fibrillation detection3 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Sensesmartwatch ECG app, inconclusive tracings counted | 66% (spec 79%)Sensitivity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Fitbit Sensesmartwatch ECG app, inconclusive tracings counted | 79%Specificity | 12-lead ECG | n = 201, Tertiary cardiology service, single-lead ECG algorithms | Mannhart et al. (2023)Funding not reported |
| Fitbit (PPG irregular rhythm algorithm)PPG irregular rhythm detection | PPV 98.2% (95% CI 95.5–99.5%)Positive predictive value | ECG patch | n = 455699, Remote trial; 1-week ECG patch after detection | Lubitz et al. (2022)Maker funded |
| Fitbit Ionic + FibriCheck algorithmthird-party PPG algorithm (FibriCheck), not Fitbit's own | Sens 97% / spec 100%Sensitivity | 12-lead ECG | n = 73, Around cardioversion, 1-min PPG | Selder et al. (2023)Independent |
VO2max estimate3 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 |
Energy expenditure (calories)5 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Versa | 8.0%–32.3% (range by intensity)Coefficient of variation | Indirect calorimetry | n = 25, Sitting, walking, running, sprints | Düking et al. (2020)Independent |
| Fitbit Sense | 13.44–29.66% (poor in all activities)Coefficient of variation | Indirect calorimetry | n = 60, Sitting, walking, running, resistance, cycling | Hajj-Boutros et al. (2023)Funding not reported |
| Fitbit Sense 2physical activity energy expenditure, 10 min | +3.14 kcalMean bias (signed) | Indirect calorimetry | n = 44, 10-min recumbent cycling intervals | Kostrna et al. (2026)Independent |
| Fitbit Surge | No device achieved EE error below 20%Study finding (no single number) | Indirect calorimetry | n = 60, Sitting, walking, running, cycling | Shcherbina et al. (2017)Independent |
More results (2)
| 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 |
1 more result in the database. Calories accuracy across devices →
Respiratory rate1 study
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| Fitbit Charge 4 | ICC 0.84 (COPD) / 0.77 (controls)Intraclass correlation | ECG chest strap (Polar H7/ | n = 55, 5 days free-living | Hermans et al. (2024)Funding not reported |
Verdict
Garmin had the edge for exercise heart rate and Fitbit for sleep in independent studies of older models. Garmin offers longer battery; Fitbit offers ECG on Charge 6 and Sense 2 and AFib evidence from the Fitbit Heart Study.
Frequently asked questions
Which is more accurate for heart rate: Fitbit or Garmin?
In Gillinov et al. (2017), the Garmin Forerunner 235 reached 0.81 concordance with ECG during exercise versus 0.67 for the Fitbit Blaze. Current models have not been compared.
Does Fitbit or Garmin have better sleep tracking?
In Schyvens et al. (2025), Fitbit Sense (κ 0.42) and Charge 5 (κ 0.41) agreed better with polysomnography than Garmin Vivosmart 4 (κ 0.21). Chinoy et al. (2021) found Fitbit Alta HR as good as or better than actigraphy and two Garmin devices worse.
Device research records
Datasets, papers and validation results for the models named on this page.