Average Testicle Size
https://www.healthline.com/health/mens-health/average-testicle-size
The dimensions of the average adult testicle are up to 2 inches long, 0.8 inches in breadth, and 1.2 inches in height (5 × 2 × 3 cm).
https://en.wikipedia.org/wiki/Testicle
Size
The relative size of testes is often influenced by mating systems.[38] Testicular size as a proportion of body weight varies widely. In the mammalian kingdom, there is a tendency for testicular size to correspond with multiple mates (e.g., harems, polygamy). Production of testicular output sperm and spermatic fluid is also larger in polygamous animals, possibly a spermatogenic competition for survival. The testes of the right whale are likely to be the largest of any animal, each weighing around 500 kg (1,100 lb).[39]
Among the Hominidae, gorillas have little female promiscuity and sperm competition and the testes are small compared to body weight (0.03%). Chimpanzees have high promiscuity and large testes compared to body weight (0.3%). Human testicular size falls between these extremes (0.08%).[40]
Testis weight also varies in seasonal breeders like deer and horses.[citation needed] The change is related to changes in testosterone production.[citation needed]
Human testicles are smaller than chimpanzee testicles but larger than gorilla testicles.[41]