The following tool can estimate your Maximal Aerobic Velocity (MAV*) and your Endurance Index* from 2 reference performances.
Computations are based on this scientific paper: 'Physiological analysis of running performance: revision of the hyperbolic model'
If you want to go deeper, you can also check more recent models: 'A minimal power model for human running performance'
(Note that any mathematical model can be challenged due to the lack of assumptions, precision and/or due to any other flaw)
Endurance Index*: values between 0 (highest endurance**) to -15 (lowest endurance**)
MAV*: velocity from which the VO2max (maximum volume of consumed oxygen) is reached
Endurance**: the ability to perform a physical activity for a long time at a given intensity