Humans are able to get an impression of the size of an object by hearing it resonate. While this ability is well described for periodic speech sounds we investigate here the ability to discriminate the size of non-periodic transient impact sounds. Three experiments were performed on normal listeners (n=19) to investigate the importance of the spectral cue in different frequency regions. Recordings from pulse resonance sounds made by a metal ball hitting polystyrene spheres of 5 different sizes were used in the experiments. Recordings were manipulated in order to show that the same cues used in speaker size discrimination are used for transient signals. Results show that the most prominent resonances are the most important cue, but frequencies above 8 kHz also contribute. The results are explained by physiologically inspired model of size discrimination that is based on the Auditory Image Model, and its key part is the Mellin transform. The model can predict which of two objects is bigger. We conclude that similar cues that are used for speaker size discrimination are important for transient sounds.