Oura calls its VO₂ max feature Cardio Capacity: an age-adjusted estimate, not a direct measurement. Its initial estimate uses profile information; for a more personalized reading, Oura offers a six-minute outdoor walking test using distance and heart rate. Garmin estimates depend on supported devices and qualifying recorded activities, while Apple Watch estimates cardio fitness during eligible outdoor walks, runs, or hikes.
Oura says its walking test is less accurate than a lab test and may not estimate high-performing athletes well. Official guidance reviewed here does not establish that Oura, Garmin, or Apple is universally more accurate, so compare what activities and inputs each feature uses rather than treating their numbers as interchangeable.
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What VO₂ max means—and what Oura calls Cardio Capacity
VO₂ max refers to the maximum amount of oxygen a person can use during exercise. It is generally expressed in milliliters of oxygen per minute per kilogram of body weight (ml/kg/min). A laboratory test measures oxygen uptake during exercise; a consumer wearable estimate is not the same as that direct test.
Oura labels its member-facing feature “Cardio Capacity.” It is an age-adjusted VO₂ max estimate. Oura’s initial estimate uses age, sex, height, and weight from the member profile and is based on population averages. That starting value is not a personal exercise-test result.
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How Oura estimates Cardio Capacity
For a more personalized reading, Oura offers a six-minute walking test. The member walks briskly outdoors while carrying a phone; location services are needed. Oura uses distance traveled and heart rate to calculate the result. The test cannot be done on a treadmill.
Oura recommends a straight, level route with few interruptions. Traffic lights and tunnels can interrupt a steady pace or GPS signal. Oura suggests taking the test about once a month to follow changes over time, but says the result is not as accurate as a lab test and may not provide a precise estimate for high-performing athletes.
The feature is available on Oura Ring Gen3 or later with an active membership on iOS and Android; it is not available on Gen2 or earlier. Oura also allows members to add a reading manually if they have a lab result or a trusted reading from another wearable.
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How Oura, Garmin, and Apple compare
| Platform | Feature name | Input described in official guidance | Conditions and caveats |
|---|---|---|---|
| Oura | Cardio Capacity, an age-adjusted VO₂ max estimate | Initial estimate from profile age, sex, height, and weight; six-minute outdoor walking test uses distance and heart rate | Test needs a phone and location services; no treadmill test. Oura says it is less accurate than a lab test and may not estimate high-performing athletes well. |
| Garmin | VO₂ max estimate | Qualifying recorded activity on supported devices; running or walking generally uses outdoor GPS or Connected GPS and heart-rate data | Requirements vary by device and activity. Cycling estimation on supported devices requires a compatible power meter. Check the exact device guidance. |
| Apple Watch | Cardio Fitness | Eligible outdoor walk, run, or hike | Apple presents levels based on age and sex. Its cited support guidance does not give a head-to-head accuracy comparison with Oura or Garmin. |
How Garmin’s estimate differs
Garmin’s estimate is available only on supported devices and qualifying activity profiles. Its support guidance describes requirements that vary by device family and activity. Running and walking generally require GPS or Connected GPS and heart-rate data; some models have specific duration or sustained heart-rate criteria. Cycling estimation on supported devices requires a compatible power meter.
This differs from Oura’s specific six-minute walking test: Garmin’s estimate is associated with recorded activities that meet the applicable device and activity criteria. Do not assume every Garmin watch calculates VO₂ max from ordinary daily wear, or that requirements are identical across models.
How Apple Watch’s Cardio Fitness estimate differs
Apple says Apple Watch can estimate cardio fitness while measuring how hard the heart and lungs are working during an outdoor walk, run, or hike. The estimate appears in the Health app. Apple describes four ranges—Low, Below Average, Above Average, and High—based on age and sex. Users can also enable low-cardio-fitness notifications.
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Apple describes estimates arising during eligible outdoor activities, rather than a prescribed six-minute test like Oura’s. Its cited support guidance does not compare its accuracy directly with Oura or Garmin.
How to get a useful Oura walking-test reading
- Check that you use Oura Gen3 or later and have an active membership.
- Choose a straight, level outdoor route where you can walk briskly with few interruptions.
- Carry your phone and make sure location services are available; Oura uses distance and heart rate for the test.
- Walk for the full six minutes. A treadmill is not supported.
- For trend tracking, Oura suggests repeating the test about once a month under similar conditions.
Oura notes that altitude may affect results and that gaps can appear when the test is not repeated. Consider the result an estimate and not a substitute for a laboratory test.
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How to interpret differences between the three
The products use different inputs and conditions: Oura offers a distinct walking test and an initial population-based estimate, Garmin uses qualifying activities on supported devices, and Apple estimates cardio fitness during eligible outdoor activity. A difference between their values does not by itself show which one is correct.
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The official guidance reviewed for this article does not provide a controlled head-to-head accuracy ranking. Oura explicitly says its walking test is less accurate than a lab test; the cited Garmin and Apple guidance describes feature requirements but does not establish a comparison with Oura. If you need a measured result, use an appropriate laboratory test rather than comparing device estimates.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.FAQ
Does Oura measure VO₂ max directly?
No. Oura calls the feature Cardio Capacity and describes it as an estimate. Its initial estimate uses profile information and population averages; its walking test uses distance and heart rate.
How long is Oura’s walking test?
The test takes six minutes. It is an outdoor walk requiring a phone and location services, and it is not supported on a treadmill.
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- ACCURACY - SMART SENSING - Oura tracks over 50 health metrics, including sleep, activity, stress, heart health, and women’s health metrics. Oura Ring 4 is powered by Smart Sensing, which adapts to you — delivering accurate, continuous data, day and night
- ACCURATE SIZING ESSENTIAL - Oura Ring 4 uses unique sizing different from standard jewelry rings; use the Oura Ring 4 Sizing Kit to find your perfect fit before purchasing
- LONG LASTING BATTERY - With up to 8 days of battery life, no screens and no vibrations, Oura Ring 4 allows you to focus on the present. From a workout to a night out — you’re free to forget it’s on. Until you start getting compliments
- OURA MEMBERSHIP - First month of membership is included with purchase, for new members only. Subscription is 5.99/mo afterwards. Membership is tied to your account via the Oura App, not your physical ring
- HSA/FSA ELIGIBLE - We can accept HSA or FSA funds for the following: Oura Ring, additional chargers, and shipping
How often should I take Oura’s walking test?
Oura suggests taking it about once a month to follow changes over time.
Can Oura’s walking test replace a lab test?
No. Oura says its walking test is not as accurate as a lab test and may not estimate high-performing athletes well.
Why might Garmin or Apple not show an estimate?
The activity may not meet the requirements for that device. Garmin’s supported devices and qualifying activity criteria vary; Apple describes estimates during eligible outdoor walks, runs, or hikes. Check the guidance for your exact device and activity.
Which is more accurate: Oura, Garmin, or Apple?
The official guidance reviewed here does not establish a universal head-to-head winner. The features rely on different activities and inputs, and Oura cautions that its walking-test estimate is less accurate than a lab test.
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