This paper presents methods for calculating short-circuit currents according to the international standard IEC 60909. Short-circuit currents need to be known in order to plan further development of the power system, adjust relay protection, dimension electrical equipment and design earthing switches. The second chapter describes the characteristic short-circuit currents, and lists the types of typical short circuits such as single-phase, two-phase, three-phase short circuits and two-phase short circuits with simultaneous connection to earth. The consequences of a short circuit such as thermal and mechanical stresses and possible ways to prevent it are also listed. The third chapter describes in detail the methods for calculating short-circuit currents: the equivalent voltage source method and the symmetrical components method. In addition, the calculation of maximum and minimum short-circuit currents is described and the equivalent impedances of electrical elements required for calculating short-circuit currents are given.