High-resolution computed tomography (CT) is the preferred noninvasive tool for diagnosing bronchiectasis in people. A criterion for evaluating dilation of the bronchus is the bronchial lumen to pulmonary artery diameter (bronchoarterial ratio [BA ratio]). A ratio of >1.0 in humans or >2.0 in dogs has been suggested as a threshold for identifying bronchiectasis. The purpose of this study was to establish the BA ratio in normal cats. Fourteen specific pathogen-free cats were selected for analysis of thoracic CT images. The BA ratios of the lobar bronchi of the left cranial (cranial and caudal parts), right cranial, right middle, left caudal, and right caudal lung lobes were measured. The mean of the mean BA ratio of all lung lobes was 0.71 ± 0.05. Individual BA ratios ranged from 0.5 to 1.11. Comparing individual lobes for each cat, there was no significant difference (P = 0.145) in mean BA ratio between lung lobes. A mean BA ratio for these normal cats was 0.71 ± 0.1, which suggests an upper cut-off normal value > 0.91 (mean ± 2 standard deviations) between normal and abnormal cats.