A lost of stability occurs on all frame structures as a result of load. This work examines the effect of load, element rigidity and shape on the stability and bracing length of multi-storey steel planar frame structures using FEM. Although the buckling is very important for the design of steel structures, in practice it is very often considered only with approximate values of buckling lengths. I have described methods for determining buckling lengths of beams in structures and have tried to provide a more precise solution. In the first chapter the theory of buckling and buckling lengths is given, in the second chapter there is the theory of stability of frame structures. The third chapter contains an overview of solving lengths using FEM. In the fourth chapter, which is the crucial point of the work, I present a practical calculation of critical buckling lengths of a given frame structure using the finite element method. The calculation analyzes the variation in the buckling lengths due to division the rods of the structure into multiple elements, changing the buckling lengths with different stiffness, and the differences in buckling lengths at different height and shape of the structure.