Music acts as a prominent element of advertising, but its simple presence does not automatically improve the effects of advertising. The concept of musical fit was developed more than 25 years ago to address the question of how music can be used effectively in advertising. However, existing empirical research on this concept has yielded inconsistent results. Recently, we developed an instrument to determine musical fit systematically in audio-visual advertising (Herget et al., 2018). To test this instrument empirically, we created six advertising stimuli (“commercials” or “ads”) representing six types of musical fit on four levels of musical fit, which varied only in terms of how many advertising reference points (spot narration, product, and/or target group) matched the background music. The findings of our between-subjects laboratory experiment (participants: 178 students, 74% female) reveal that the stimuli at different levels of musical fit differed sharply in terms of the intuitively perceived degree of musical fit (η2 = .33). In addition, increasing the level of musical fit improved advertising efficiency in terms of participants’ attitudes toward the ad (η2 = .12) and product (η2 = .12), as well as their purchase intentions (η2 = .06) and memory performance (η2 = .06). If other researchers were to use the instrument described, which defines and operationalizes musical fit systematically and transparently, results of future empirical studies would be more consistent. The results of the present study indicate that advertisers are well advised to select music to fit the commercial’s reference points as closely as possible, to intensify the music’s efficiency.