To determine the accuracy of orchidometry and ultrasonography for measuring the testicular volume by comparing the resultant measurements with the actual testicular volume in humans.

The testicular volume of 40 testes from 20 patients with prostate cancer (mean age ± SD 74.5 ± 7.5 years) was measured using the Prader orchidometer and ultrasonography before therapeutic bilateral orchiectomy. The ultrasound measurements of testicular volume were calculated using three formulas: length (L) × width (W) × height (H) × 0.52, L × W² × 0.52, and L × W × H × 0.71. The actual testicular volumes were determined by water displacement of the surgical specimen.

The mean actual testicular volume of the 40 testes was 9.3 cm³ (range 2.5 to 23.0). A strong correlation was found between the testicular volume calculated by the three ultrasound formulas and the actual volume (r = 0.910 to 0.965, P <0.0001) and was stronger than the correlation with the Prader orchidometer (r = 0.818, P <0.0001). The smallest mean difference from the actual testicular volume was observed with the formula L × W × H × 0.71, which overestimated the actual volume by 0.80 cm³ (7.42%). The measurements using the Prader orchidometer correlated with the actual testicular volume and with the testicular volume calculated using the three ultrasound formulas (r = 0.801 to 0.816, P <0.0001). However, the orchidometer measurements had the largest mean difference from the actual testicular volume (6.68 cm³, 81.7%).

The results of this study have shown that measuring the testicular volume by ultrasonography is more accurate than by the Prader orchidometer, and the formula L × W × H × 0.71 was the most accurate for calculating the testicular volume.