Martin in 1983 and 1985 used a formula to estimate the average enamel thickness. This formula has not been tested since then. To test his formula we used tooth-shaped geometric standards. We found that the method of defining the average enamel thickness (T) as c/e (1) by Martin is incorrect. To correct MartinÂs definition, a reasonable approximation for arc-like segments would be 2c/d+e where d+e is the perimeter of the enamel, c the area of the sectioned enamel and e the length of the enamel dental junction. For other than arc-like segments in the enamel other formulas should be applied rendering the estimation of average enamel thickness a complicated matter. Consequently, cladograms and phylogenetic trees based on formula (1) should be revised.