OBJECTIVE The purpose of this study was to assess patient comfort when rinsing for 30 s with 5, 10, 15, 20 or 30 ml volumes of mouthwash, with the goal of establishing the most agreeable volume. METHODS The study was designed as a single-blind, clinical trial with duplicate assessments. Participants were asked to rinse with five different volumes of mouthwash in randomized order. All participants received a questionnaire to evaluate their attitudes towards the volumes used based on a Visual Analogue Scale (VAS). The extremes of the VAS were 0 (far too little) to 10 (far too much), with a score of five representing the optimal score. After 1 week, the participants returned, and the assessment was repeated to evaluate the validity of the estimate. Volumes were tested for differences regarding participants' perceptions of comfort using anova and paired t-tests, and the duplicate answers of the participants were analysed for validity by calculating the Pearson correlation coefficient. RESULTS In total, 62 participants completed both assessments, which provided valuable data. The 15-ml volume resulted in a mean score of 5.40, whereas the 5, 10, 20 and 30 ml volumes resulted in mean scores of 1.89, 3.71, 6.54 and 8.65, respectively. The differences between the mean scores for all five tested volumes were statistically significant. A correlation between the first and second VAS scores was 0.4-0.6. CONCLUSIONS On the basis of the results of this experiment, it can be concluded that 15 ml is perceived as the most comfortable volume.