The temperature rise calculation of core-type power transformers is an essential question in the design process however this is neglected during the preliminary optimization process. The methods of the calculation methods are classified and introduced shortly and they applicability is examined for the preliminary design process. For comparison of the methods performance, two core arrangements were examined, the Roth's transformer and a 50 MVA three-phase transformers' core. The result shows that the FEM method provides the most accurate solution however according to its simplicity, the Ryder's method has better performance in the preliminary design stage.