The effects of four parameters (speed, fundamental frequency, repetition units, and inharmonicity) on perceived urgency were scaled using an application of Stevens's power law. From the exponents obtained, equal units of urgency change were calculated for three parameters. The units were combined in a set of stimuli, and the order of urgency was predicted. The obtained and predicted orders of urgency were highly correlated. The results also showed that even when equalized by psychophysical techniques, some parameters contribute more to perceived urgency than do others. This may be attributable to the different types of parameters scaled or the proportion of the usable range of each parameter that represents a unit change in urgency. The implication of the work for the design and improvement of auditory warnings is discussed.