This master thesis describes the properties and capabilities of the XGSLab software package and its modules. The aim was to independently calculate the magnetic field strength in this software package, study its applications and describe its use. The second chapter describes the properties of the electromagnetic field according to Maxwell's equations in differential form. The magnetic field of the electric current and the quantities that describe it are further explained in more detail. The effects of the magnetic field on human beings according to Directive 2013/35 / EU of the European Parliament and of the Council are then described. The main physical quantities and regulations that must be observed according to the Ordinance on protection against electromagnetic fields are also listed. The tables give the limit values of magnetic field strength and magnetic flux density for public areas and areas of increased sensitivity. The third chapter provides a detailed description of the XGSLab software package: its GSA and GSA_FD modules for analysis of earthing systems, XGSA_FD and XGSA_TD for overhead and underground earthing systems analysis in the frequency domain, as well as in the time domain, and NETS for calculation and simulation of multi-conductor and multi-phase complex networks. The areas of application of this software package, its applications and possibilities are listed, starting from standard references, waveform, soil modeling, all the way to data analysis and presentation of results. At the end of this chapter, the calculation of the magnetic field strength is described and the already solved examples of the distribution of magnetic flux density in space for different elements of the power system in the XGSA_FD module are presented. In the fourth chapter, examples of the calculation of the magnetic field strength, i.e. magnetic flux density using the XGSLab software package for three-phase overhead line and cable are solved. All the steps necessary for the successful execution of the calculation are listed and the obtained results are presented.