The severity of chronic obstructive pulmonary disease (COPD) is evaluated not only by airflow limitation but also by factors such as exercise capacity and body mass index. Recent advances in CT technology suggest that it might be a useful tool for evaluating the severity of the disease components of COPD. The aim of this study is to evaluate the correlation between the parameters measured on volumetric CT, including the extent of emphysema, air trapping, and airway thickening, and clinical parameters. CT scans were performed in 34 patients with COPD at full inspiration and expiration. We used in-house software to measure CT parameters, including volume fraction of emphysema (V950), mean lung density (MLD), CT air trapping index (CT ATI), segmental bronchial wall area (WA), lumen area (LA), and wall area percent (WA%). We found that the CT parameters were correlated with the pulmonary function test (PFT) results, body mass index (BMI), the modified Medical Research Council Dyspnea scale (MMRC scale), the six-minute-walk distance (6MWD), and the BODE index. V950 insp correlated to the BMI, FEV1, 6MWD, and the BODE index. The CT ATI correlated with the physiologic ATI (VC - FVC) (R = 0.345, p = 0.045) and the MMRC scale (R = 0.532, p = 0.001). There was a positive correlation between the WA% and the BMI (R = 0.563, p < 0.001). MLDexp showed the strongest correlation with the BODE index (R = -0.756, p < 0.001). We conclude that the severity of emphysema and air trapping measured on CT correlated with the PFT parameters 6MWD and BMI.