Domain wall resonances of different domain configurations occuring in thin garnet films are recorded with a magneto-optic spectrometer under cw excitation. The measured resonance frequencies are used to evaluate the effective domain wall mass density m. The necessary restoring pressure constants are obtained using both experimental and theoretical methods. Generally, m is found to be substantially higher than mD, the infinite flat wall mass density. We obtain m/mD between 1.4 and 2.2, with highest values observed for parallel stripes. © 1982.