Puberty
The first sign of puberty in boys is that their testicles (also called the testes) and scrotum (the "bag" that the testicles are in) grow bigger. Before puberty, each testicle is about 1.5 to 2 cm (0.6 to 0.8 in) long and  a volume of about 2 to 3 cubic centimetres (cc) (0.1 to 0.2 cubic inches (cu in)). About six years after puberty starts, the testicles reach their adult size. The volume of an average adult man's testicle is about 18 to 20 cc (1.1 to 1.2 cu in). However, it is normal for some men to have testicles smaller than this size, and for other men to have larger testicles.