Unsolved problems in the field of hot gas cleaning led to a renewed interest in the performance of cyclone dust separators. Various calculation procedures exist for the calculation of cyclones. Most of these models need high calculation expenditure. For practical cyclone design a rough calculation of the separation efficiency and the energy consumption is often sufficient. This paper presents two possibilities to calculate the grade efficiency and the pressure drop. The first one is easy to handle but is based on simplified physical assumptions. The second one is a more complex calculation procedure which uses a detailed physical description of the flow field and considers turbulence, re-entrainment and the secondary flow. The results of the two calculation models are compared with experimentally obtained data for different gas temperatures.