orchidometer

An orchidometer is a medical instrument used to estimate testicular volume in males. It consists of a cord or string bearing a series of beads of known volumes, typically ranging from 1 to 25 milliliters. The most common form is the Prader orchidometer, named after Arnold Prader, and it is widely used as a quick bedside tool in clinical settings.

To use, a clinician palpates the testis through the scrotal skin and visually compares its size with the beads until a closest match is found. The estimated testicular volume is read from the bead that best matches the testis. The measurement is an approximate estimate and can be affected by observer experience and anatomical factors such as scrotal contents or edema. Because of variability, orchidometer measurements are considered less precise than ultrasound.

Applications include assessing gonadal development during puberty, evaluating disorders of puberty and hypogonadism, monitoring testicular growth in pediatric patients, and contributing to infertility workups. Although convenient and rapid, orchidometer measurements should be interpreted with caution and, when precise assessment is necessary, complemented or replaced by ultrasound measurements that use standardized formulas to calculate volume. The orchidometer remains a common, widely used tool in urology, pediatrics, and endocrinology for a quick appraisal of testicular size.