Although organ weight gives pathologists information about the pathogenesis of diseases at autopsy, the knowledge is rarely helpful in postmortem virtual autopsy by computed tomography (CT). To investigate the feasibility of liver weight estimation based on liver volume estimated from three-dimensional CT images and the specific gravity of liver, thirty cadavers who died in the University of Fukui Hospital and whose family members agreed to postmortem CT and autopsy were prospectively enrolled. Mean specific gravity of liver was 1.054 ± 0.009 g/mL (95% confidence interval: 1.0507–1.0573 g/mL). The specific gravity was positively correlated to Hounsfield unit (HU) values of less than 40 (cases with moderate to severe fatty deposition) and remained stable between 1.05 to 1.065 g/mL for HU values greater than 40 (cases with mild or no fatty change). The liver weight estimated by our formula corresponded well to the actual liver weight, and the correlation coefficient was 0.96 (P< 1 × 10−13). The estimated liver weight calculated from estimated liver volume and the specific gravity of 1.055 g/mL was highly accurate, whereas the specific gravity should be reduced by 2%–3% in patients with an HU value less than 40 due to fatty deposition.