This paper presents a numerical method for predicting thermoelastic damping (TED) in micromechanical resonators with any arbitrary structural geometry. In this numerical method, TED is interpreted as the generation of thermal energy per cycle of vibration from the viewpoint of thermal field. Consequently, TED is mathematically expressed in terms of entropy — a parameter measuring the irreversibility in heat conduction, and then numerically calculated in ANSYS/Multiphysics. The validity of this numerical method has been verified using the well-known solution to TED in a beam resonator and experimental data in the literature. Compared to the commonly used interpretation of TED in the elastic field-complex frequency, this numerical method does not involve complex values and thus offers the advantages of simplicity and compatibility with finite element modeling software.