Thermo-elastic deformation of the machine tool due to thermal expansion of machine components presents one of the biggest challenges in maintaining accuracy and product quality. The operation of the machine inevitably leads to waste heat due to friction losses of bearings and guides and electrical losses of motors and control cabinets. These internal heat sources lead to inhomogeneous and changing temperature fields, which also interact with the ambient temperature. An interaction with the environment takes place via natural or forced convection and radiation. During the design phase, these thermal effects are determined using thermal (typically FEM) simulations. For existing machines, thermal measurements are possible but require careful planning and execution. Thermo-elastic FEM simulations coupled with thermal measurements in a climate chamber with controlled ambient and foundation temperature, lead to an optimal understanding and management of thermal errors in machine tools. In this paper, the process of thermo-elastic FEM in connection with measurement principles in a climate chamber will be presented. The five-axis milling machine tool DMU 80 evo is used to demonstrate and validate the results of the thermo-elastic FEM with measurement data.