This study aimed to identify the optimal method for evaluating coronary artery calcium (CAC) severity on non-electrocardiogram-gated low-dose chest computed tomography (LDCT) within the Korean Lung Cancer Screening (K-LUCAS) project. Four cardiothoracic radiologists independently assessed CAC severity using four different scoring methods and classified severity for each case as none, mild, moderate, or severe. The interobserver agreement was found to be moderate for visual assessment and substantial for the other three methods. Agreement between the four grading methods for the same observer was substantial for three observers and moderate for one. The mean evaluation time varied significantly between methods. The study concluded that artery-based grading could be appropriate due to its substantial interobserver agreement and acceptable mean evaluation time. The K-LUCAS project has been managed by Coreline Soft Inc and the study used the AVIEW Research image review platform.