As explained in the book "Daniels' Running Formula" by Jack Daniels, PhD, the term VDOT is a measure of your running ability based strictly on race performance. It can be considered a sort of "effective" VO2max, which is more useful than the lab-determined value because it also incorporates your running economy, lactate response, and perhaps even your motivation and willingness to deal with discomfort! VDOT comes from two curves developed by Daniels and Gilbert: one that describes how oxygen consumption varies with running speed, and another that gives the maximum intensity a runner can sustain for any set time. For each distance, you just draw both curves and look for the time where they cross. Unfortunately, the equations for these curves are so complex that an exact solution is not possible. Undaunted by this, I devised a numerical approach that converges to the unique solution for each distance in about 4 iterations. me if you are interested in the gory details. To use my VDOT calculator, select a distance and enter the time required to run that distance in a race or all-out effort. Click the first button to calculate your VDOT, then click the second button to calculate your expected race times for other distances.
The source code for this application is available for free - just ask!