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VO2max calculator from a race time or resting heart rate
VO2max, the most oxygen your body can use per minute, is measured in a lab with a mask on a treadmill. Outside the lab it can only be estimated. This calculator offers the two estimates with the best track record that need no equipment: one from a recent race, one from your maximum and resting heart rate. Compare the result with the Cardio Fitness value your Apple Watch records.
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Short answer
From a race: a 5K in 20:00 corresponds to a VO2max (VDOT) of about 49.8 ml/kg/min, a 10K in 50:00 to about 40. From heart rates: VO2max ≈ 15.3 × maximum heart rate ÷ resting heart rate, so 190 and 50 bpm give about 58. Both are estimates; the race-based one is usually the better guide for runners.
Two ways to estimate VO2max
From a race (Daniels and Gilbert)
Coach Jack Daniels and physiologist Jimmy Gilbert fitted two equations to lab and race data: one for the oxygen cost of running at a given speed, one for the share of VO2max a runner can hold for a given race duration. Divide the first by the second and you get the VO2max your race performance implies. Daniels calls it VDOT and uses it to set training paces. It includes your running economy, so an efficient runner gets a higher value than a lab test might show. That is why it predicts race times well. The calculator accepts races from 1.5 km to the marathon, the range the equations were built for.
From heart rates (Uth)
A Danish study by Niels Uth and colleagues (2004) found that the ratio of maximum to resting heart rate tracks VO2max in trained men: VO2max ≈ 15.3 × HRmax ÷ HRrest. It needs no race, but it depends heavily on an accurate maximum heart rate and has a wide error for individuals. Treat it as a ballpark figure, and prefer the race estimate when you have one.
Comparing with Apple Watch Cardio Fitness
Apple Watch estimates VO2max as Cardio Fitness during outdoor walks, runs and hikes and shows values from 14 to 65 ml/kg/min in the Health app. The watch uses your heart rate and pace on the move, so it measures something close to the race estimate, but it can differ by several points, especially if most of your runs are slow, on hills or on a treadmill. Where to find it and how to read it: VO2max on Apple Watch.
One value matters less than its direction. Keho shows your VO2max trend over months next to your training load, so you can see whether a block of training actually moved it.
How to raise VO2max
Two kinds of training move it: plenty of easy aerobic volume, the Zone 2 base, and a smaller dose of hard intervals of three to five minutes near your maximum. Untrained people improve fastest; after years of training, gains are small and economy and threshold matter more for race times.
Questions
Is a higher VO2max always better?
It sets the ceiling, not the result. Two runners with the same VO2max can race very differently because of economy and how close to that ceiling they can hold a pace.
Can I predict race times from the result?
Yes, from the race-based value, but going straight from one race to another is simpler and just as accurate. Use the race time predictor.
Is this medical advice?
No. These are fitness estimates for healthy, active adults, not a medical assessment.