Background <p>Sleeve gastrectomy is an effective bariatric procedure; however, postoperative outcomes vary among patients. Residual gastric volume has been proposed as an anatomical factor influencing weight loss and surgical success. Three-dimensional computed tomography volumetry enables accurate postoperative assessment of gastric volume. The aim of the work was to evaluate residual gastric volume after laparoscopic sleeve gastrectomy using three-dimensional computed tomography volumetry and to correlate it with postoperative outcomes, particularly percentage of excess weight loss.</p> Methods <p>This retrospective observational study included 20 adult patients who underwent laparoscopic sleeve gastrectomy. Postoperative three-dimensional computed tomography gastric volumetry was performed, and residual gastric volume was calculated. Weight loss outcomes were assessed using percentage of excess weight loss. Correlation analysis and receiver operating characteristic curve analysis were used to evaluate the relationship between residual gastric volume and surgical outcomes.</p> Results <p>The mean residual gastric volume was 345.7&#xa0;mL, and the mean percentage of excess weight loss was 52.4%. Successful weight loss was achieved in 75% of patients. A significant negative correlation was observed between residual gastric volume and percentage of excess weight loss (<i>r</i> =  − 0.62, <i>p</i> &lt; 0.001). Receiver operating characteristic analysis identified a residual gastric volume cutoff of 250 mL for predicting surgical success, with 80% sensitivity and 85% specificity.</p> Conclusion <p>Residual gastric volume measured by three-dimensional computed tomography volumetry is a significant predictor of postoperative outcomes after laparoscopic sleeve gastrectomy and may aid in postoperative assessment and risk stratification.</p>