In many hydraulic calculations it is necessary to define roughness coefficients (Manning's-n). This work should simplify the selection of a proper roughness coefficient for open channels. The first part of the work describes basic hydraulic principles and also the importance of roughness coefficients. The next chapter provides a comprehensive overview of completed studies and their results. Many table values as well as figures aid the easier selection of a proper roughness coefficient. Furthermore the study includes detailed calculations and a summary of the results for selected flow cross-sections. Close to discharge sites the slope and the flow velocity has been measured. Based on that data and using collected information from the hydrographic office of Burgenland ("Wasserportal Burgenland") and the homepage ehyd from the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management (BMLFUW) it was possible to calculate roughness coefficients for several discharges. The results were verified by using different calculation methods (MANNING formula, DARCY-WEISBACH equation, INDLEKOFER, COWAN and EINSTEIN and HORTEN). This enabled a comparison of the measured with the recalculated values. Finally, for the Tauchenbach in Altschlaining, a roughness coefficient was estimated by using the conducted studies. It was possible to compare the results.