This article motivates the loss characterization and modeling of Class II multilayer ceramic capacitors (MLCCs), which have been widely utilized owing to high energy density, in high-frequency resonant converters. In a resonant tank, MLCCs experience complex electrical operating conditions (e.g., large-signal, high-frequency, dc bias), but the incurred power loss has not been clearly characterized and modeled. This article first proposes a novel resonant-Sawyer–Tower circuit, which can experimentally extracts the loss of an MLCC in real operation in a resonant tank. A general loss modeling approach named Steinmetz's pre-electrified graph (SPeG) is then proposed to correlate capacitor's loss to the peak value of excitation, frequency, and dc bias voltage. The SpeG model provides the material-specific volume loss density of common class II dielectric materials and can be easily extrapolated to evaluate the loss of the MLCCs with different rated voltage and capacitance but employing the same dielectric material. To generalize the material-specific SPeG model to device-level application, this article also proposes an easy-to-follow tool, dielectric thickness observer (DTO), to estimate the internal microstructural geometry by tracking the - characteristic provided in product datasheet. The synergy of the proposed characterization circuit, SPeG loss model, and DTO establishes a toolkit that enables the estimation of MLCC losses in a manner similar to that of a ferromagnetic inductor/transformer core. This article is accompanied by microscope images of the investigated MLCC samples and MATLAB scripts of the proposed DTO.