This paper discussed methods of estimation of cutting tool quantum required for serial processing of a set of work pieces: (1) at a particular work point, mid (2) in two alternative cases associated with automatic lines. The first case covers failure to replace single cutting tools, while the second variant handles simultaneous replacement of all cutting tools after a certain working time, -By introduction of cost, the optimum replacement time is made determinable, i.e. it is possible to estimate the number of tools required to process a defined quantity of work pieces at the observed operation point,