Smartwatch VO2max Accuracy
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.
In lab tests against indirect calorimetry, three Garmin models estimated VO2max with mean absolute percentage errors of 7.05% to 7.9%, and three Apple Watch studies found 13.2% to 15.79%. Pixel Watch 3 recorded 8.65% in a Google-funded study. Ultrahuman has only a company-written preprint.
Which wearable is most accurate for VO2max?
8 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 Watch3 studies, n = 89
- OuraNo published validation found
- WHOOPNo published validation found
- Garmin3 studies, n = 78
- FitbitNo published validation found
- Pixel Watch1 study, n = 34No independent validation
- SamsungNo published validation found
- PolarNo published validation found
- WithingsNo published validation found
- AmazfitNo published validation found
- Ultrahuman1 study, n = 101No independent validation
- COROSNo published validation found
VO2max estimate: mean absolute percentage error (%)
Reference: Indirect calorimetry. Lower is better. 7 studies; a device tested in more than one study shows its median.
- 1Garmin Fenix 67.05%1 study, n = 19 (7.05% (CCC 0.73)) · Carrier et al. (2025)
- 2Garmin Forerunner 920XT7.3%1 study, n = 24 (7.3%) · Passler et al. (2019)
- 3Garmin Forerunner 2457.9%1 study, n = 35 (7.9% / 7.2% (two runs)) · Engel et al. (2026)
- 4Google Pixel Watch 38.65%1 study, n = 34 (8.65% (bias −0.53 mL/kg/min)) · Lambe et al. (2026)Maker funded
- 5Apple Watch Series 1013.2%1 study, n = 40 (13.2% (MAE 6.79 mL/kg/min)) · Lambe et al. (2026)
- 6Apple Watch13.3%1 study, n = 30 (13.31% (MAE 6.92 mL/kg/min)) · Lambe et al. (2025)
- 7Apple Watch Series 715.8%1 study, n = 19 (15.79% (ICC 0.47)) · Caserman et al. (2024)
All published results
Every VO2max 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).
VO2max estimate8 studies
| Device tested | Result | Reference | Sample | Study |
|---|---|---|---|---|
| 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 |
| 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 |
| 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 |
| Google Pixel Watch 3 | 8.65% (bias −0.53 mL/kg/min)Mean absolute percentage error | Indirect calorimetry | n = 34, Free-living VO2max estimate vs maximal treadmill test | Lambe et al. (2026)Maker funded |
| Ultrahuman Ring AIR | MAE 4.68 mL/kg/min (r 0.79)Mean absolute error | Indirect calorimetry | n = 101, Single-site CPET cohort; model developed on 85, tested on 16 | Dhawale et al. (2026)Preprint · maker authored |
- Apple Watch Series 1013.2% (MAE 6.79 mL/kg/min)
Mean absolute percentage error · vs Indirect calorimetry · n = 40, Maximal treadmill test (modified Åstrand)
Lambe et al. (2026) Independent
- Apple Watch13.31% (MAE 6.92 mL/kg/min)
Mean absolute percentage error · vs Indirect calorimetry · n = 30, Maximal treadmill test (modified Åstrand)
Lambe et al. (2025) Independent
- Apple Watch Series 715.79% (ICC 0.47)
Mean absolute percentage error · vs Indirect calorimetry · n = 19, Graded cycle ergometer test
Caserman et al. (2024) Independent
- Garmin Forerunner 2457.9% / 7.2% (two runs)
Mean absolute percentage error · vs Indirect calorimetry · n = 35, Treadmill ramp test
Engel et al. (2026) Funding not reported
- Garmin Fenix 67.05% (CCC 0.73)
Mean absolute percentage error · vs Indirect calorimetry · n = 19, Graded exercise test and outdoor run
Carrier et al. (2025) Independent
- Garmin Forerunner 920XT7.3%
Mean absolute percentage error · vs Indirect calorimetry · n = 24, Lab
Passler et al. (2019) Independent
- Google Pixel Watch 38.65% (bias −0.53 mL/kg/min)
Mean absolute percentage error · vs Indirect calorimetry · n = 34, Free-living VO2max estimate vs maximal treadmill test
Lambe et al. (2026) Maker funded
- Ultrahuman Ring AIRMAE 4.68 mL/kg/min (r 0.79)
Mean absolute error · vs Indirect calorimetry · n = 101, Single-site CPET cohort; model developed on 85, tested on 16
Dhawale et al. (2026) Preprint · maker authored
Read before comparing
- VO2max is an estimate built from heart rate, pace or power and your profile. It needs outdoor runs or walks with GPS, and errors depend on how the watch was set up.
- Studies used different maximal tests (treadmill or cycle ergometer) and small samples (19 to 40 people).
- The Ultrahuman Ring AIR preprint has not been peer reviewed and was written by company staff, so it is listed but never ranked.
- 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.
Download the wearable accuracy table (CSV)
Every leaderboard row with study, DOI, reference standard and sample size. We'll email you the link.
FAQ
Which smartwatch is most accurate for VO2max?
In published lab tests, Garmin estimates were closest: 7.05% (Fenix 6, Carrier 2025), 7.3% (Forerunner 920XT, Passler 2019) and 7.9% (Forerunner 245, Engel 2026) mean absolute percentage error. Apple Watch studies found 13.2% (Series 10), 13.31% and 15.79% (Series 7). These are different studies with different protocols.
Is the Ultrahuman Ring VO2max estimate validated?
Only in a 2026 medRxiv preprint by Ultrahuman staff: a model developed on 85 people and tested on 16 reported a mean absolute error of 4.68 mL/kg/min. It has not been peer reviewed or independently replicated.