Garmin vs Pixel Watch & Fitbit: VO2max compared
How Garmin and Pixel Watch & Fitbit estimate your VO2max, what each needs from you, what else they show and what independent studies say about accuracy.
| Garmin | Pixel Watch & Fitbit | |
|---|---|---|
| Called | VO2 Max. | VO2 max (called Cardio Fitness Score before 2026) |
| Algorithm | Garmin in-house, built on Firstbeat Analytics | Not disclosed |
| App | Garmin Connect | Google Health app (called the Fitbit app until May 19, 2026) |
| From: Outdoor run | Yes | Yes |
| From: Walk | Yes | No |
| From: Treadmill | No | No |
| From: Bike (power meter) | Yes | No |
| From: Resting test | Not confirmed | No |
| From: All-day data | Not confirmed | No |
| Fitness age | Yes | Not confirmed |
| Race predictor | Yes | Not confirmed |
| Published accuracy studies | 5 | 3 |
| What you need to do | Run outdoors with GPS for at least 10 minutes at 70%+ of max heart rate, or ride steadily at high intensity for 20+ minutes with a power meter. Set up your user profile and max heart rate. | An outdoor run of at least 10 minutes with GPS. If no value appears, you may need up to three runs in 30 days. |
Key differences
- Garmin can estimate from walk, bike (power meter); Pixel Watch & Fitbit can't.
- Fitness age: Garmin shows one (not confirmed for the other).
- Race predictions: Garmin has them.
- Accuracy evidence: we found 5 published studies for Garmin and 3 for Pixel Watch & Fitbit.
How each one works
Garmin: Compares your heart rate (wrist or chest strap) with your GPS pace on outdoor runs, or with power from a power meter on rides. It learns over several activities, so early numbers may be off.
Pixel Watch & Fitbit: The app compares your running pace with your heart rate during outdoor GPS runs, then compares that running efficiency with your resting heart rate. Since 2026 it no longer uses height and weight to calculate the score, and it can include runs from connected third-party apps.
Which is better for VO2max?
For VO2max specifically, the best device is the one that sees your hardest efforts: if most of your training is outdoor running, both give an estimate (both use outdoor run). If you cycle with a power meter, walk more than you run, or want a resting test, check those rows above. Whichever you choose, compare the number with itself over time and with the norms for your age.
Accuracy studies
Garmin
- Howard et al., J Med Eng Technol, 2026: Forerunner 265 overestimated VO2max (43.95 vs 41.10 ml/kg/min at start) but mean absolute percent error stayed under 10%.
- Engel et al., Eur J Appl Physiol, 2026: Forerunner 245 underestimated VO2max by about 4-5 ml/kg/min (MAPE 7.2-7.9%); error was larger in highly trained athletes (MAPE 9.4-10.4%).
- Carrier et al., Sensors, 2025: fēnix 6 VO2max estimates were judged accurate (MAPE 7.05%, concordance 0.73 vs 30 s lab average).
- Düking et al., J Sports Sci Med, 2024: Forerunner 245 in youth soccer players: MAPE 5.58% after one run and 1.06% after a second run.
- Passler et al., Int J Environ Res Public Health, 2019: Forerunner 920XT had a MAPE of 7.3% but significantly underestimated VO2max.
Pixel Watch & Fitbit
- Lambe et al., PLoS One, 2026: Pixel Watch 3 vs lab treadmill test (n=34): bias -0.53 mL/kg/min, limits of agreement -12.56 to 11.50, MAPE 8.65%. Funded by Google.
- Klepin et al., Med Sci Sports Exerc, 2019: Fitbit Charge 2 vs lab VO2max (n=60): bias +1.59 (15 s data) and +0.30 mL/kg/min (60 s data), MAPE under 10%.
- Freeberg et al., mHealth, 2019: Fitbit Charge 2 (n=30) overestimated: 52.5 vs 49.9 mL/kg/min measured, ICC 0.87, MAPE 10.2%.
Frequently asked questions
Is Garmin or Pixel Watch & Fitbit more accurate for VO2max?
Garmin has more published validation (5 vs 3 studies). Watch estimates are typically within several ml/kg/min of lab tests for groups, with larger individual errors, so use either one to track your trend.
Does Garmin measure VO2max from outdoor run like Pixel Watch & Fitbit?
Yes: both estimate from outdoor run.
Which is better for VO2max: Garmin or Pixel Watch & Fitbit?
Pick the one whose data sources match how you train: Garmin uses outdoor run, walk, bike (power meter); Pixel Watch & Fitbit uses outdoor run.
Built from official documentation (see each brand page for sources). Features vary by model and firmware. Garmin and Pixel Watch & Fitbit are trademarks of their owners; VO2max Health is independent and not affiliated with either.