In this article the strength analyses of weights boxes are presented. Boxes are designed as a welded steel structure at which weights with total mass almost ten tons are stored in them. These boxes are an integral part of a mechanism intended for calibration of the mass measurement device. The article contains on one hand the basic scope of the theory of elasticity and strength analysis and on the other hand the numerical computations of the structure by using the Finite Element Method. Based on results the structure of weights boxes was modified in order to satisfy the defined safety factor.