How to Accurately Determine Testicular Volume Without Ultrasound

The most commonly used clinical methods can overestimate volumes by 250 percent, but a new calculator gives providers much more reliable values.

Columbus, OH — January 2018

Testicular volume is important in diagnosing and tracking disorders of puberty in adolescence and in assessing fertility for adults. Ultrasound is the gold standard for determination of volume – but it requires specialized equipment and extra cost for the patient. The most frequently used clinical methods to determine volumes, orchidometers or external measures in the scrotum, overestimate volumes by as much as 80 percent for adults, 150 percent for pubertal boys and 250 percent for prepubertal boys, because of the inclusion of the scrotal skin and epididymis.

So Juan Sotos, MD, an endocrinologist at Nationwide Children’s Hospital, has developed a new equation, and an accompanying calculator, to give much more accurate values. Studies detailing his work have recently been published in the International Journal of Pediatric Endocrinology.

“If you are evaluating a boy going through puberty, you don’t want to pay for an ultrasound every time you need a volume,” says Dr. Sotos, who is also an emeritus professor of Pediatrics at The Ohio State University College of Medicine. “This calculator allows a provider to measure the width of the testis during physical examination with a centimeter ruler, enter that value and the genital development stage, and obtain a volume equivalent to the volume that would be found with ultrasound.”

The calculator is freely available at

The typical equation for clinical methods uses lengths and widths, but does not adjust for scrotal skin and epididymis. Dr. Sotos developed his formula by including the ratios of length over width and thickness over width obtained in ultrasound.  In that manner, the scrotal skin and epididymis are excluded. He determined the volumes of 318 testes in 159 subjects, age 3 to 34 years. 

The new formula is (Width-Scrotal Skin)³ x 0.88. The calculator subtracts the scrotal skin for the genital development stage entered.

The utility for pediatric endocrinologists is clear, but adult providers (including primary care physicians) could also easily use the calculator to screen for disorders and fertility.

“To take just one example, about 75 percent of patients who have Klinefelter syndrome are never diagnosed,” says Dr. Sotos. “If you were a primary care doctor, and you measured the testes and found an abnormally small size, you could potentially help detect that condition. Testicular volume really should be a part of the physical examination, and this calculator makes it easier to determine volumes.”


Sotos JF, Tokar NJ. Appraisal of testicular volumes: volumes matching ultrasound values referenced to stages of genital development. International Journal of Pediatric Endocrinology. 17 July 2017. [Epub ahead of print]

Sotos JF, Tokar NJ. A medical calculator to determine testicular volumes matching ultrasound values from the width of the testis obtained in the scrotum with a centimeter ruler. International Journal of Pediatric Endocrinology. 21 November 2017. [Epub ahead of print]