Estimate your VO2 max from a recent race result using the Daniels and Gilbert equations, or from a 12-minute Cooper test. Both run entirely in your browser. The number you get is an estimate derived from performance rather than a measurement, which is worth understanding before you put much weight on it.
| Distance | Time | Pace |
|---|
What VO2 max is, and what this number actually is
VO2 max is the maximum rate at which your body can take in and use oxygen during exercise, measured in millilitres per kilogram of body weight per minute. Measuring it properly means a laboratory, a mask, and gas analysis while you run to exhaustion.
What this calculator gives you is not that. It works backwards from a performance, and a performance depends on more than aerobic capacity — running economy and the fraction of your maximum you can hold for the duration both matter. Jack Daniels was explicit about this and called his metric VDOT, a pseudo VO2 max. Two runners with identical laboratory values can produce different VDOT scores because one of them wastes less energy at the same pace.
That is a feature rather than a flaw if you are using the number to guide training. VDOT predicts what you will actually run better than a lab value would, precisely because it bundles in economy. It is simply not the same quantity, and it is worth knowing which one you are looking at.
The two methods this calculator uses
From a race result, it uses the Daniels and Gilbert equations, published in Oxygen Power (1979) and carried through Jack Daniels’ later work. One curve converts running velocity into an oxygen cost; a second estimates what fraction of maximum you can sustain for a given duration. Dividing one by the other gives VDOT.
From a 12-minute test, it shows two numbers, and they will not match. Cooper’s original regression — distance in metres minus 504.9, divided by 44.73 — comes from his 1968 paper in JAMA (203:201-204), validated against treadmill testing in 115 US Air Force personnel with a correlation of about 0.90. The Daniels figure treats your 12 minutes as a race and runs it through the same equations as any other result.
They disagree, and not randomly. Across the range most people cover in twelve minutes, Cooper’s regression returns the higher number — around four points higher at 2,000 m, widening to roughly nine points at 3,600 m. Cooper’s equation was fitted in 1968 to Air Force personnel, many of them not distance runners; the Daniels equations came from competitive runners. Neither is wrong, and the size of the gap is a fair picture of how much precision a field estimate of this kind actually carries.
Which should you use? If you are comparing yourself against published Cooper norm tables, use the Cooper figure, because those tables were built around that equation. If you want a number you can compare against a VDOT derived from a race, use the Daniels figure. The one thing not to do is take whichever is higher because you prefer it.
Why your watch shows a different number
Garmin, Apple, Polar and Coros all estimate VO2 max continuously from the relationship between your heart rate and your pace during ordinary runs. That method never requires a maximal effort, which is convenient, but it inherits every source of heart rate error: optical sensor lag, heat, caffeine, cardiac drift on long runs, hills, and a maximum heart rate the watch has probably guessed from your age.
A race-derived figure has the opposite profile. It needs one hard, honest effort, and in exchange it depends on nothing but a distance and a stopwatch. If the two disagree, the race-based number is usually the one to trust, provided the race was genuinely maximal. Our heart rate zone calculator covers how much slack sits in an age-estimated maximum heart rate, which is the main thing feeding your watch’s version.
What the equivalent times mean
Because VDOT ties every distance to a single number, a result at one distance implies a result at all the others, and the table projects those. It is a genuinely useful sanity check: if your half marathon time is far slower than your 5 km implies, the gap is usually endurance rather than speed, and that tells you what to train.
The projections assume you have actually prepared for the distance. A runner with a strong 5 km and thirty kilometres a week will not run the projected marathon time, and no equation can fix that. Treat the longer projections as a ceiling that training still has to earn.
When these estimates are unreliable
- The effort has to be maximal. A tempo run, a parkrun you jogged, or a race you faded badly in produces a number that means nothing. If you had anything left at the finish, the estimate reads low.
- Very short efforts are noisier. Results from about 3 km upwards give more reliable estimates. A 1500 m leans heavily on anaerobic contribution that these equations do not model well.
- Fitness moves. Use a result from the last four to eight weeks. A personal best from two years ago describes a different person.
- Cooper’s equation was derived in men. The original validation used male Air Force personnel, and later work extending it to women has been comparatively thin. The Daniels figure alongside it is a useful cross-check.
- This is running only. Cycling has a different economy and a different relationship between power and oxygen cost, so neither equation transfers. Cyclists estimating aerobic fitness should work from functional threshold power instead.
- Course and conditions matter. Heat, wind, hills and altitude all cost you time that the equations will simply read as lower fitness.
Why VO2 max is not the whole picture
Among untrained people, VO2 max separates the fit from the unfit fairly well. Among trained endurance athletes it separates much less than its reputation suggests. Runners with similar values routinely race minutes apart, because the fraction of maximum they can hold and how efficiently they move differ more than their ceilings do.
This matters for what you do with the number. Chasing VO2 max specifically means short, very hard intervals, and there is a limit to how far that goes. Threshold work and accumulated easy volume raise the fraction of your maximum you can sustain, which for most people is where the available improvement actually sits. Our zone 2 training guide covers the easy end of that, and the heart rate zone calculator will set the bands.
Gear for tracking this across a training block
You need no equipment to use this calculator — a race result and a stopwatch are enough. If you want your watch’s continuous estimate to be less noisy, the highest-value change is feeding it accurate heart rate: our Polar H10 review covers the reference chest strap, and the heart rate monitor guide covers the wider field.
For the running side, our running watch guide and budget running watch guide cover which models track VO2 max trends usefully rather than just displaying a number that drifts.
Frequently asked questions
Is VDOT the same as VO2 max?
No. VDOT is a performance index that combines aerobic capacity with running economy, which is why Daniels described it as a pseudo VO2 max. It predicts race performance better than a laboratory value does, but it is not the same measurement.
Which race distance gives the best estimate?
Something between 3 km and the half marathon, run hard and recently. Shorter races lean on anaerobic capacity these equations model poorly; marathons depend so heavily on fuelling and durability that one bad day distorts the result.
Why do the Cooper and Daniels numbers differ on my 12-minute test?
They are separate regressions fitted to different data, so they diverge systematically rather than randomly. Cooper’s reads higher across the whole realistic range, by about four points at 2,000 m and nine at 3,600 m. His came from Air Force personnel in 1968; Daniels’ came from competitive distance runners. Pick one and stay with it rather than switching between them.
What is a good VO2 max?
It depends heavily on age and sex, and the single-number thresholds circulating online rarely say which population they came from. A more useful approach is to track your own figure across training blocks using the same method each time, where the trend means considerably more than the absolute value.
Can I use this if I only cycle or row?
Not reliably. Both equations are built on the oxygen cost of running. Cyclists are better served by functional threshold power, and rowers by a 2000 m test scored against rowing-specific tables.