Abstract: Fatigue failure of an engineering article is primarily influenced by a natural inherent defect in the material from which the article is made. By an ability established to allocate a quantitative measure to such defect as a new material property influenced only by environment and material manufacturing procedures as are other basic properties, and using known methods for determining critical stress areas, a wide range of fatigue design data can be generated from a few basic measurements. Thus, from the deduction of a characteristic material defect length, there can be determined both a material's basic fatigue properties and the fatigue capability of the article for which the material is used.