Device comparisons
WHOOP vs Garmin: Sleep and Heart Rate Accuracy from a Published Study
In Miller et al. (2022, 53 adults), WHOOP 3.0 agreed more closely with ECG overnight (HR ICC 0.99 vs 0.41) and with polysomnography sleep stages (60% vs 50%) than the Garmin Forerunner 245. WHOOP supplied raw data and funds the lab.
Published study results
| Metric | WHOOP 4.0 | Garmin (Forerunner 265 / Forerunner 965 / Fenix 8) |
|---|---|---|
| Overnight heart rateICC vs ECGMiller et al. 2022, n=53 | 0.99WHOOP 3.0Closer in this study | 0.41Forerunner 245 |
| Sleep stagesEpoch agreement vs PSGMiller et al. 2022, n=53 | 60%κ 0.44 · WHOOP 3.0Closer in this study | 50%κ 0.25 · Forerunner 245 |
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
WHOOP 4.0
Screenless bandDevice guideGarmin (Forerunner 265 / Forerunner 965 / Fenix 8)
Sports watchDevice guideWHOOP 4.0 Onyx SuperKnit band: product photograph from WHOOP’s listing. 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
Miller et al. 2022 tested six devices on 53 adults for one night. WHOOP supplied raw data and the lab receives WHOOP research support. Figures are for WHOOP 3.0 and Forerunner 245, not every WHOOP or Garmin model.
| Specification | WHOOP 4.0 | Garmin (Forerunner 265 / Forerunner 965 / Fenix 8) |
|---|---|---|
| Overnight heart rateICC vs ECG | 0.99WHOOP 3.0Closer in this study | 0.41Forerunner 245 |
| Sleep stagesEpoch agreement vs PSG | 60%κ 0.44 · WHOOP 3.0Closer in this study | 50%κ 0.25 · Forerunner 245 |
Primary rows only. The study tables further down list more results from the accuracy database.
Hardware specs
| Specification | WHOOP 4.0 | Garmin (Forerunner 265 / Forerunner 965 / Fenix 8) |
|---|---|---|
| Battery LifeDiffers | Five days | Up to 13 days (FR265); 23 days (FR965); 16 days (Fenix 8 47 mm AMOLED) |
| GPSDiffers | No (uses phone) | Yes |
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: Miller et al. 2022, Sensors (six devices vs PSG and ECG, n=53), Chinoy et al. 2021, Sleep (seven sleep trackers vs PSG), Bellenger et al. 2021, Sensors (WHOOP HR and HRV vs ECG), WHOOP: Introducing WHOOP 4.0, Garmin Forerunner 265 owner's manual: battery information, Garmin Forerunner 965 owner's manual: battery information, Garmin Fenix 8 owner's manual: battery information, Garmin: Understanding HRV Status.
Pros and cons
WHOOP 4.0
Pros
- Overnight HR and HRV ICC 0.99 vs ECG for WHOOP 3.0 (Miller 2022)
- Sleep-stage agreement 60% (κ 0.44) for WHOOP 3.0
- Strain score from 0 to 21
Cons
- No GPS or screen
- Five-day battery
- Requires a membership
Garmin (Forerunner 265 / Forerunner 965 / Fenix 8)
Pros
- Up to 13 days (FR265), 23 days (FR965), 16 days (Fenix 8 47 mm AMOLED)
- Built-in GPS and screen
- HRV Status vs a 3-week baseline
Cons
- Forerunner 245 overnight HR ICC 0.41 vs ECG (Miller 2022)
- Garmin Fenix 5S and Vivosmart 3 did 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 rest2 studies
Only maker-funded evidence for WHOOP on this metric.
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP | ≤ 0.39 ± 0.38%Mean bias (signed) | ECG | Rest, 15 opportunities | Bellenger et al. (2021)Maker funded |
| Garmin Vivoactive 4 | ρc = 0.9998Lin's concordance correlation | ECG | n = 263, 30-min standardised recording | Theurl et al. (2023)Independent |
Heart rate during exercise5 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 3.0 | High agreement only in squats; low in rows and burpeesStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 29, Resistance exercise (5 exercises) | Støve et al. (2022)Funding not reported |
| WHOOP 4.0 (upper arm) | Strongest agreement (with Verity Sense) in graded treadmillStudy finding (no single number) | ECG chest strap (Polar H7/ | n = 28, Rest, warm-up, burpees, Bruce treadmill | Moghaddam et al. (2025)Funding not reported |
| 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 |
More results (1)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 |
Overnight heart rate2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 4.0 | 3.00%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| WHOOP 4.0 | 0.91Lin's concordance correlation | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| WHOOP 3.0 | ICC 0.99Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Maker funded |
| WHOOP 3.0 | 0.7 bpm (absolute bias)Mean absolute error | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Maker funded |
More results (2)
| 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)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 4.0 | 8.17%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| WHOOP 4.0 | 0.94Lin's concordance correlation | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
| WHOOP | Ln RMSSD 1.66 ± 1.80% (LoA ±5.93%)Mean bias (signed) | ECG | Rest, 15 opportunities | Bellenger et al. (2021)Maker funded |
| WHOOP 3.0 | ICC 0.99Intraclass correlation | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 3.0 | 4.7 ms (absolute bias)Mean absolute error (absolute bias) | ECG | n = 53, Overnight, sleep laboratory | Miller et al. (2022)Maker funded |
| Garmin Fenix 6 | 10.52%Mean absolute percentage error | ECG | n = 13, Home, during sleep, 536 nights | Dial et al. (2025)Independent |
4 more results in the database. HRV accuracy across devices →
Sleep stages (4-stage)4 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP (strap, 2.0 era) | 64% (κ 0.47)Epoch-by-epoch agreement | Polysomnography (PSG) | n = 12, Sleep laboratory, 10-day protocol, 86 sleeps | Miller et al. (2020)Funding not reported |
| WHOOP (strap, 2.0 era) | κ = 0.47Cohen's kappa | Polysomnography (PSG) | n = 12, Sleep laboratory, 10-day protocol, 86 sleeps | Miller et al. (2020)Funding not reported |
| WHOOP (auto-detect) | 63%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 6, Sleep laboratory, 9 nights, 54 sleeps | Miller et al. (2021)Maker funded |
| WHOOP 3.0 | 60%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 3.0 | κ = 0.44Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Maker funded |
| WHOOP 4.0 | κ = 0.37Cohen's kappa | Polysomnography (PSG) | n = 40, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
3 more results in the database. Sleep accuracy across devices →
Sleep vs wake (2-stage)5 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 4.0 | > 90% (all devices)Sensitivity | Polysomnography (PSG) | n = 62, Sleep laboratory, 1 night | Schyvens et al. (2025)Funding not reported |
| WHOOP (strap, 2.0 era) | 89% (κ 0.49)Epoch-by-epoch agreement | Polysomnography (PSG) | n = 12, Sleep laboratory, 10-day protocol, 86 sleeps | Miller et al. (2020)Funding not reported |
| WHOOP (strap, 2.0 era) | κ = 0.49Cohen's kappa | Polysomnography (PSG) | n = 12, Sleep laboratory, 10-day protocol, 86 sleeps | Miller et al. (2020)Funding not reported |
| WHOOP (auto-detect) | 86%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 6, Sleep laboratory, 9 nights, 54 sleeps | Miller et al. (2021)Maker funded |
More results (2)
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP 3.0 | 86%Epoch-by-epoch agreement | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Maker funded |
| WHOOP 3.0 | κ = 0.44Cohen's kappa | Polysomnography (PSG) | n = 53, Sleep laboratory, 1 night, 9 h in bed, all devices worn together | Miller et al. (2022)Maker funded |
5 more results in the database. Sleep accuracy across devices →
Total sleep time2 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| WHOOP (strap, 2.0 era) | +8.2 ± 32.9 min (n.s.)Mean bias (signed) | Polysomnography (PSG) | n = 12, Sleep laboratory, 10-day protocol, 86 sleeps | Miller et al. (2020)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)5 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 |
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)3 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 |
Verdict
For overnight recovery data, WHOOP 3.0 outperformed the Forerunner 245 in the one study that tested both, with the funding caveat noted. For GPS training, a screen and battery measured in weeks, Garmin is the practical choice.
Frequently asked questions
Is WHOOP or Garmin more accurate for sleep?
In Miller et al. (2022), WHOOP 3.0 matched polysomnography sleep stages in 60% of epochs (κ 0.44) versus 50% (κ 0.25) for the Garmin Forerunner 245. Chinoy et al. (2021) also found two older Garmin devices worse than actigraphy for sleep/wake.
Is WHOOP Recovery Score better than Garmin Body Battery?
No study has validated either composite score against a reference. The underlying overnight heart rate agreed more closely with ECG for WHOOP 3.0 (ICC 0.99) than for Forerunner 245 (0.41) in Miller et al. (2022).
Has anyone compared WHOOP and Garmin during exercise?
Not in the studies we verified; Miller et al. (2022) measured overnight only.
Device research records
Datasets, papers and validation results for the models named on this page.