What this calculates
VO2 max — maximal oxygen uptake — is the maximum rate at which your body can consume oxygen during exhaustive exercise. It's one of the strongest predictors of endurance running performance. This calculator estimates VO2 max and the related VDOT value from a race time using the Daniels-Gilbert equation.
Jack Daniels, a physiologist and running coach, developed the VDOT concept in his 1979 paper with Jimmy Gilbert as a way to express equivalent performance across distances. VDOT is not the same as VO2 max, though the values are numerically close for trained runners. VDOT is effectively a "performance-derived VO2 max" — calculated purely from what you ran, not from a laboratory test.
The Daniels-Gilbert formula calculates VO2 at race pace as a percentage of VO2 max, accounting for the percent VO2 max that can be sustained at different race durations. The calculation involves two components: the velocity-to-VO2 curve (which converts running speed to oxygen demand) and the fraction of VO2 max that can be sustained at a given duration (which peaks around 10–15 minutes and decreases for longer races).
VDOT tables are most useful for identifying equivalent performances across distances and for setting training paces. A runner with VDOT 50 can predict a 17:50 5K, a 37:03 10K, a 1:21:46 half marathon, or a 2:54 marathon — all roughly equivalent race efforts. The training pace zones (Easy, Marathon, Threshold, Interval, Repetition) derived from VDOT are used by coaches following the Daniels system.
This calculator shows your estimated VO2 max, your VDOT, and equivalent performances at standard distances using the Daniels tables.
How to use this calculator
Enter a recent race time in H:MM:SS or MM:SS format and the race distance. Use a race run at full effort — a parkrun, a road race, or a timed trial on a flat measured course.
The calculator shows your estimated VO2 max and VDOT, plus equivalent predicted performances at 5K, 10K, half marathon, and marathon. It also shows recommended training paces (Easy, Threshold, Interval) derived from your VDOT.
For most useful results, use a race at a distance between 5K and marathon where you genuinely raced to the limit of your ability on that day.
Methodology
Implements the Daniels-Gilbert 1979 equation as described in Jack Daniels' "Running Formula" (4th ed., Human Kinetics, 2021). VO2 at a given velocity: VO2 = −4.60 + 0.182258v + 0.000104v². Percentage of VO2 max sustainable at duration t: %VO2max = 0.8 + 0.1894393e^(−0.012778t) + 0.2989558e^(−0.1932605t). VDOT = VO2 / %VO2max. Race time predictions use the inverse computation from VDOT through the Daniels tables.
Full methodology and formula sources →
Frequently asked questions
What is the difference between VDOT and VO2 max?
VO2 max is a physiological measurement of maximum oxygen uptake, measured in a laboratory under controlled conditions. VDOT is derived from race performance — it produces a numerically similar value but is not the same measurement. A runner's lab VO2 max and their performance-derived VDOT often differ by a few points, due to running economy differences.
Why does my VDOT differ between distances?
VDOT should be consistent across your best performances at different distances if you're equally well-trained for all. If your 5K VDOT is much higher than your marathon VDOT, you're likely undertrained in endurance relative to speed. If your marathon VDOT is higher, you have strong endurance but may be speed-limited. Use your most recent, best-effort race at any distance.
Can I use a training run time?
Only if it was a true all-out effort on a measured flat course. Easy runs will produce artificially low VDOT values. A parkrun personal best, a timed race, or a solo 5K time trial run at race effort are all suitable inputs.
What are the Daniels training zones?
Jack Daniels defines five training intensities: Easy (E), Marathon (M), Threshold (T), Interval (I), and Repetition (R). Each is expressed as a pace derived from VDOT. Easy pace is where 80%+ of training volume occurs; Threshold is around your lactate threshold pace; Interval is at approximately VO2 max pace; Repetition is faster than VO2 max pace.
How accurate are VDOT race time predictions?
VDOT predictions are most accurate within ±1–2 adjacent standard distances (10K from half marathon, half from marathon) for trained runners who race similarly across distances. Predictions break down when the base race was run in unusual conditions, when the runner has a large strength-endurance imbalance, or when significant training has occurred between races.