The cardiothoracic ratio (CTR) is considered to be a reliable detector of cardiomegaly on computed tomography for livings, with a threshold of 0.5. Our study aimed to establish an adjusted CTR-based score to predict cardiac hypertrophy at PMCT. We selected adult's autopsy cases examined between 2009 and 2016. Two groups were considered, a normal heart weight group and an overweighed heart group. The CTR was measured on axial images. Logistic regression analysis was performed to investigate the discriminating power of the CTR between groups when adjusted to the confounding factors. Sixty-six cases with normal heart weight and 94 cases with overweighed heart were analyzed. The factors associated to the cardiac hypertrophy are CTR (p value 0.003, OR 3.57), BMI (p value 0.055, OR 1.09), age (p value < 0.001, OR 1.67), and gender (p value 0.002, OR 4.85). The area under the ROC curve (receiver operating characteristic curve) was 0.77 when using CTR alone and 0.88 when considering BMI, age, and gender. In conclusion, CTR alone cannot be used to discriminate between normal heart weight and overweighed heart at PMCT. A new formula has been developed, including age, gender, and BMI. Dilatation of the cardiac chambers, which is a subjective evaluation, influences the CTR measure and could be not related to a pre-existing cardiac hypertrophy. This new score formula allows to overpasses this subjective step. We proposed a cut-off value of the score of 32 for the diagnosis of cardiac hypertrophy. The Internet/smartphone application (http://calc.chuv.ch/CTR) facilitates its routine application.