An analysis has been made of the factors involved in the A.S.T.M. Trapezoid Tear-Strength Test. The tear strength of a fabric measured by this test is dependent mainly on the extensibility of the threads, the breaking strength of the threads, the effective specimen length, and the number of threads per inch of fabric. An analytical interpretation of the part played by each of these factors resulted in a general equation relating tear strength to the breaking strength and extensi bility of a given fabric. The evaluation of the derived equation gave a good correlation between the calculated and measured tear-strength values of the fabrics investigated.