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Wearable HRV Accuracy Leaderboard

Reviewed by Sameer Sontakey, Co-founder and Chief AI & Algorithms Officer at Sensor Bio. ChatPPG is independent and device-neutral; it is not a Sensor Bio product.

Against multi-lead ECG at rest, HRV4Training (4.10% MAPE) and Oura (6.84% MAPE) had the lowest rMSSD errors reported by Stone et al. (2021); the camera-based CameraHRV app had 112.36% MAPE.

Which wearable is most accurate for HRV?

30 published results from 8 studies in the wearable accuracy database. Each ranking below compares devices only on the same statistic against the same kind of reference. Results from different statistics or references are never ranked together.

Evidence by brand

  • Apple Watch2 studies, n = 92
  • Oura4 studies, n = 120
  • WHOOP3 studies, n = 66
  • Garmin3 studies, n = 329
  • FitbitNo published validation found
  • Pixel WatchNo published validation found
  • SamsungNo published validation found
  • Polar3 studies, n = 95
  • WithingsNo published validation found
  • AmazfitNo published validation found
  • UltrahumanNo published validation found
  • COROSNo published validation found

HRV (RMSSD): mean absolute percentage error (%)

Reference: ECG. Lower is better. 3 studies; a device tested in more than one study shows its median.

  1. 1HRV4Training (app)4.1%1 study, n = 5 (4.10%) · Stone et al. (2021)
  2. 2Oura Ring 45.96%1 study, n = 13 (5.96%) · Dial et al. (2025)
  3. 3Oura Ring6.84%1 study, n = 5 (6.84%) · Stone et al. (2021)
  4. 4Oura Ring Gen37.15%1 study, n = 13 (7.15%) · Dial et al. (2025)
  5. 5WHOOP 4.08.17%1 study, n = 13 (8.17%) · Dial et al. (2025)
  6. 6Garmin Fenix 610.5%1 study, n = 13 (10.52%) · Dial et al. (2025)
  7. 7Polar Grit X Pro16.3%1 study, n = 13 (16.32%) · Dial et al. (2025)
  8. 8Apple Watch Series 9 / Ultra 228.9%1 study, n = 39 (28.88% (MAE 20.46 ms)) · O'Grady et al. (2024)
  9. 9CameraHRV (app)112.4%1 study, n = 5 (112.36%) · Stone et al. (2021)

HRV (RMSSD): intraclass correlation

Reference: ECG. Higher is better. 2 studies; a device tested in more than one study shows its median.

  1. 1WHOOP 3.00.991 study, n = 53 (ICC 0.99) · Miller et al. (2022)Maker funded
  2. 2Polar Vantage V20.9311 study, n = 29 (ICC 0.931 (nocturnal LnRMSSD)) · Nuuttila et al. (2021)Maker funded
  3. 3Somfit0.691 study, n = 53 (ICC 0.69) · Miller et al. (2022)
  4. 4Apple Watch Series 60.671 study, n = 53 (ICC 0.67) · Miller et al. (2022)
  5. 5Polar Vantage V0.651 study, n = 53 (ICC 0.65) · Miller et al. (2022)
  6. 6Oura Ring Gen20.631 study, n = 53 (ICC 0.63) · Miller et al. (2022)
  7. 7Garmin Forerunner 245 Music0.241 study, n = 53 (ICC 0.24) · Miller et al. (2022)

HRV (RMSSD): lin's concordance correlation

Reference: ECG. Higher is better. 2 studies; a device tested in more than one study shows its median.

  1. 1Oura Ring 40.991 study, n = 13 (0.99) · Dial et al. (2025)
  2. 2Oura Ring Gen30.971 study, n = 13 (0.97) · Dial et al. (2025)
  3. 3WHOOP 4.00.941 study, n = 13 (0.94) · Dial et al. (2025)
  4. 4Garmin Fenix 60.871 study, n = 13 (0.87) · Dial et al. (2025)
  5. 5Polar Grit X Pro0.821 study, n = 13 (0.82) · Dial et al. (2025)
  6. 6Garmin Vivoactive 40.6621 study, n = 263 (ρc = 0.66 (moderate)) · Theurl et al. (2023)

HRV (RMSSD): mean absolute error (absolute bias) (ms)

Reference: ECG. Lower is better. 1 study.

  1. 1WHOOP 3.04.7 ms1 study, n = 53 (4.7 ms (absolute bias)) · Miller et al. (2022)Maker funded
  2. 2Polar Vantage V18.8 ms1 study, n = 53 (18.8 ms (absolute bias)) · Miller et al. (2022)
  3. 3Oura Ring Gen218.9 ms1 study, n = 53 (18.9 ms (absolute bias)) · Miller et al. (2022)
  4. 4Apple Watch Series 622.5 ms1 study, n = 53 (22.5 ms (absolute bias)) · Miller et al. (2022)
  5. 5Somfit24 ms1 study, n = 53 (24.0 ms (absolute bias)) · Miller et al. (2022)
  6. 6Garmin Forerunner 245 Music33.1 ms1 study, n = 53 (33.1 ms (absolute bias)) · Miller et al. (2022)

Head-to-head results within single studies

Devices tested side by side in one study, on the same people and protocol.

Ranked: lower is better

rMSSD mean absolute percent error (MAPE) vs ECG, lower is better

Stone JD, et al. (2021), Frontiers in Sports and Active Living. doi:10.3389/fspor.2021.585870

5 adults, 148 trials · Reference: Multi-lead ECG · Resting-state HR and rMSSD

  1. 1HRV4Training (app)CCC 0.984.10%
  2. 2Oura RingBrand guideCCC 0.916.84%
  3. 3CameraHRV (app)CCC 0.04112.36%

All published results

Every HRV result in the database, including statistics that cannot be ranked. Download the full table as CSV for all rows. From the wearable accuracy database (v1.0.0).

HRV (RMSSD)8 studies

18 more results in the database.

Download all results (CSV)

Read before comparing

  • Stone et al. tested seven devices, but the abstract reports rMSSD numbers only for these three; the rest are in the full paper.
  • Small sample (5 participants, 148 trials) at rest only.
  • Rankings combine studies only when they report the same statistic against the same kind of reference, and still differ in protocol and population. Treat close values as ties.

FAQ

Which wearable measures HRV most accurately?

In Stone et al. (2021), the lowest resting rMSSD errors were HRV4Training (4.10% MAPE) and Oura (6.84% MAPE) versus multi-lead ECG.

Are camera HRV apps accurate?

Not in this study: CameraHRV had a rMSSD MAPE of 112.36% and concordance of 0.04 against ECG.

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