The article considers the determination of the final contours of the open pits. One of the problems of development of iron ore deposits at the present stage of development of opencast mining is described, which consists in the fact that in most open pits their working contours on the surface have reached final position. In these conditions, it is necessary to reevaluate the capabilities of the raw material base for further operation of mining enterprises. The analysis of scientific achievements in the decision of the final definition of the open pits` contours is executed. The well-known principle of determining the boundaries of opencast mining, the principle of which is to determine the boundaries based on a comparison of the allowable cost of ore production with the expected for the designed open pit. On the example of the open pits, which reflect the characteristic features of the development of steep-dipping deposits of Ukraine, the influence of current overburden ratio of the existing open pits on the economic overburden ratio, which serves as the main criterion in determining the boundaries of opencast mining for the designed open pits. A method for determining the boundaries of the open pits has been developed, which provides for the use of the economic overburden ratio of opening as a value not constant but variable over time, and one that depends on the change of current coefficients of opening in open pits-competitors. As a result, the theory in the field of determining the final contours of the open pits is improved. The new method differs from the known ones by taking into account the change in the economic overburden ratio over time, as well as determining the impact of technological indicators of open pits -competitors on the final depth of the designed open pit.