When performing a physical examination in the andrology clinic, accurate measurement of testicular size is important. Two methods for measuring testicular size have been developed using calipers for measurement and comparison with plastic testicular models. We have developed a new orchiometer, which consists of a graded series of punched-out elliptical rings with the volume of the ellipsoids indicated on each ring. Testicular sizes measured by our orchiometer had a better correlation with real testicular size determined by water displacement of testes after castration when compared with those data obtained by using calipers. By the use of this orchiometer, the normal range of the adult testicular size was greater than 14 ml in Japan and greater than 17 ml in the United States. This orchiometer is valuable for the rapid and accurate assessment of sexual maturation in children and men.