Our implementation of dielectric-loss spectroscopy consists of placing a sample inside a resonant microwave cavity and measuring the change in cavity characteristics caused either as a function of ground or excited-state solute concentration. Electromagnetic modeling is then used to relate the complex permittivity of the sample to the resonator properties, allowing quantitative permittivity measurements. The modeling is combined with quantitative simulation of the dipolar relaxation time to extract the molecular dipole moment and polarizability volume of the solute. [SI section COMSOL Simulation of Microwave Cavities]