The high-frequency operating characteristics of inductors are determined by their stray capacitance, which can lead to current ringing and electromagnetic interference. The research on the stray capacitance of inductor windings is relatively mature; however, there is limited research on the capacitance related to magnetic cores. The electric field intensity in the air gaps of magnetic cores can be relatively high, making the energy capacitance nonnegligible. Therefore, this paper proposes an approximate calculation method for the boundary potential of distributed air gaps in rod NiZn magnetic cores. The model is verified using finite element analysis (FEA), providing a reference for the design of gapped inductors.