Key takeaways
A cardio fitness score is an estimate of VO2max in ml/kg/min, the oxygen your body can use at maximal effort, shown against people of your age and sex
Devices differ: Fitbit and Garmin use GPS runs, Apple adds walks and hikes, Oura uses a six-minute walk test, WHOOP mixes sleep and activity data, and Polar uses a five-minute rest test
Labels are not interchangeable, since each brand uses its own reference data and number of levels, so compare yourself with yourself on one device
"Cardio fitness score", "Cardio Capacity", "Cardio Fitness", "VO2 Max": wearable brands use different names for the same idea. Each is an estimate of your VO2max, the most oxygen your body can use during hard exercise, in millilitres per kilogram per minute. None of them measures oxygen. Here is how each device gets its number and what its labels mean. For the basics, see what is VO2max?
What is a cardio fitness score?
Most methods rely on one fact: fitter people have a lower heart rate at the same speed. Devices that watch you run or walk compare heart rate with pace. Devices that only see you at rest use resting heart rate, heart rate variability and your profile, which a 2022 meta-analysis found less accurate: resting-based estimates tended to overestimate VO2max, while exercise-based ones were closer on average.
How each device estimates and labels it
| Device | Name in the app | How it is estimated | Labels |
|---|---|---|---|
| Fitbit and Pixel Watch (Google Health app) | VO2 max, formerly cardio fitness score | Outdoor GPS runs of 10 minutes or more: pace against heart rate, compared with resting heart rate | Poor, Fair, Average, Good, Very good, Excellent |
| Apple Watch | Cardio Fitness | Outdoor Walk, Outdoor Run or Hiking workouts, plus age, sex, weight, height and medications | Low, Below Average, Above Average, High |
| Garmin | VO2 max | Outdoor GPS runs of 10 minutes or more at 70% or more of max heart rate, or rides with a power meter | Poor (red), Fair (orange), Good (green), Excellent (blue), Superior (purple) |
| Oura | Cardio Capacity | First a population estimate from age, sex, height and weight, then a six-minute walking test using phone GPS and heart rate | Low, Fair, High, Peak |
| WHOOP | VO2 Max | Sleep-time resting physiology, activity, sleep and demographics; outdoor GPS runs and lab results refine it | Number in ml/kg/min |
| Polar | Fitness Test (OwnIndex) | Five minutes lying still: resting heart rate, heart rate variability, profile and training background | Very low, Low, Fair, Moderate, Good, Very good, Elite |
Cardio fitness score Fitbit
In May 2026 the Fitbit app became the Google Health app, and Google renamed cardio fitness score to VO2 max. The help page says it is now measured only on outdoor runs with GPS, not walks, rides or treadmill sessions, and Google notes that the score is no longer calculated from demographics such as height and weight. You need a 10-minute outdoor run, and up to three runs in 30 days, for a first reading. Longer, faster runs on flat ground help. Find it in the Fitness tab under Key metrics.
Cardio fitness score by age
Here are the Fitbit and Google Health ranges for the Average level and the start of Excellent, in ml/kg/min:
| Age | Men: Average | Men: Excellent from | Women: Average | Women: Excellent from |
|---|---|---|---|---|
| 20–30 | 42.7–48.6 | 60.4 | 35.9–40.8 | 50.2 |
| 30–40 | 38.9–44.2 | 55.0 | 32.1–36.5 | 44.9 |
| 40–50 | 35.0–39.8 | 49.4 | 28.2–32.0 | 39.5 |
| 50–60 | 31.1–35.4 | 44.0 | 24.2–27.4 | 33.9 |
| 60+ | 27.2–31.0 | 38.7 | 20.3–23.0 | 28.4 |
Other brands use other reference data, so the same number can earn a different label. Apple uses the FRIEND registry and Garmin the Cooper Institute. Our VO2max chart and VO2max norms by age and sex explain the main norm sets.
Oura Cardio Capacity
Oura calls Cardio Capacity an "age-adjusted estimate" of VO2max. Until you do a test, the number comes only from your profile and population averages. The six-minute walking test uses distance from your phone's GPS and your heart rate, so walk briskly on a straight, level route without traffic lights or tunnels; it cannot be done on a treadmill. Oura suggests repeating it about once a month, and you can also enter a lab or other wearable value. Find it under My Health > Heart Health > Cardio Capacity (Gen3 or later, with membership). It is separate from Oura's Cardiovascular Age, which comes from pulse-wave signals.
WHOOP VO2 max
WHOOP describes a three-tier model. The passive estimate uses resting physiology measured during sleep, activity volume and intensity, sleep behaviours and demographics, and needs at least 14 recoveries in the previous 21 days. If you logged an outdoor GPS run in the last 90 days, pace and heart-rate response are added. If you enter a lab test result, it anchors future estimates. In WHOOP's own validation of 248 people, the average error was 3.7 ml/kg/min (8.0%) for the passive model and 3.3 ml/kg/min (7.1%) with GPS runs. These are company figures, not an independent study.
Apple, Garmin and Polar
Apple and Garmin both compare heart rate with speed during exercise; see our guides to Apple Watch VO2max and Garmin VO2max. Polar's Fitness Test works at rest, so it suits people who do not run. Polar's white paper reports a mean error of 8.2% (3.7 ml/kg/min) against lab tests in its development study, which recorded heartbeats with a dedicated recorder rather than an optical wrist sensor.
How to use your score
- Stick to one device and judge the trend over 4 to 8 weeks. See how accurate is your watch's VO2max estimate?
- Keep your profile correct: weight, age and max heart rate all feed the estimate.
- Raise it with training: intervals plus easy volume. See how to improve VO2max and HIIT vs steady cardio, and set zones with the heart rate zone calculator.
- Cross-check: try our VO2max calculator, VO2max running calculator or fitness age calculator.
- Need a real measurement? See VO2max tests explained.
Fitbit, Google, Pixel, Oura, WHOOP, Apple, Garmin and Polar are trademarks of their respective owners. VO2max Health is independent and not affiliated with or endorsed by any of them.
Frequently asked questions
What is a cardio fitness score?
It is a wearable's estimate of your VO2max, the most oxygen your body can use during hard exercise, in ml/kg/min. Fitbit used the name until 2026, when the Google Health app renamed it VO2 max.
What is a good cardio fitness score by age?
On the Fitbit and Google Health scale, Average for men runs from about 42.7 to 48.6 ml/kg/min at 20 to 30 and 35.0 to 39.8 at 40 to 50. For women it is about 35.9 to 40.8 and 28.2 to 32.0. Anything above that is Good or better.
Is Oura cardio capacity accurate?
Oura says its six-minute walking test is not as accurate as a lab test and may be less precise for high-performing athletes or at high altitude. Without a walking test, the first number is only a population estimate from age, sex, height and weight.
How does WHOOP calculate VO2 max?
WHOOP combines resting physiology measured during sleep, activity, sleep habits and your age, sex, height and weight. If you log outdoor GPS runs, it adds pace and heart rate, and you can anchor it with a lab test result.
Sources
- Google Health Help. Learn about your VO2 max.
- Google Health Help. What is new with the redesigned Google Health app.
- Oura Help. Cardio Capacity (VO2 Max).
- Oura. ŌURA announces two new heart health features, 2024.
- WHOOP. How accurate is WHOOP VO₂ Max? The science behind the estimate.
- Apple Support. Track your cardio fitness levels.
- Apple Watch User Guide. Monitor your heart health on Apple Watch.
- Garmin. Forerunner 965 Owner's Manual: About VO2 Max. Estimates.
- Polar. Vantage V3 User Manual: Fitness test.
- Polar. Polar Fitness Test white paper.
- Molina-Garcia P, et al. Validity of estimating the maximal oxygen consumption by consumer wearables: a systematic review with meta-analysis and expert statement of the INTERLIVE network. Sports Med, 2022.