Our purpose was to assess the correlation between the estimated volume based on ultrasonic measurement in vivo and the actual weight of the diseased uterus after hysterectomy, and then retrospectively tried to establish a simple equation to convert the volume into the weight in grams. A total of 105 women with nonmalignant diseased uteri which were prepared to undergo laparoscopy-assisted vaginal hysterectomy had had preoperative ultrasound scanning to estimate the uterine size by measuring three dimensions including the length (L), width (W) and anteroposterior (AP) diameter. The uterine volume was calculated by the use of a prolate ellipsoid formula (4/3 × π × L/2 × W/2 × AP/2). Actual uterine weight was immediately taken after extirpation of the uterus. Linear regression analysis revealed uterine weight (g) = 50.0 + 0.71 × volume (cm3), with correlation coefficient = 0.93 and SE = 49.6 g. There was a close, positive correlation between the estimated uterine volume and actual uterine weight. With utilization of this equation, the uterine size in vivo can thus be expressed as a concrete, objective value in weight instead of ‘weeks’ size’ by comparison with pregnant uterus, which has been commonly used in traditional gynecologic practice.