Abstract: Microring resonators serve as pivotal components for the generation of microcavity optical frequency combs, and their thermal characteristics significantly affect the stable excitation and operational sustainability of these combs. This research examines two silicon nitride microring resonators with a twofold difference in diameter, elucidating the influence of resonator size on thermal effects via a thermal dynamics model and pump laser scanning experiments. The findings indicate that the smaller microring resonator, due to its lower heat capacity and thermal conductance, experiences a more pronounced temperature increase during laser pumping. Moreover, it exhibits a greater thermal triangular skew and more substantial resonance drift. As a result, enlarging the size of the microring resonator effectively mitigates these thermal effects. This study offers valuable insights into the quantitative assessment of microring size on thermal behavior, aiding in the optimization of microring thermal stability and improving the excitation efficiency of microcavity frequency combs.