| TANNER STAGE |
Typical testicle volume and fertility | Penis development |
Artist's impression of genitalia (when loosely circumcised) | Annual height gain | Comments |
|---|---|---|---|---|---|
| Stage 1 | Under 4 ml Not fertile at least whilst orgasms, if any, remain dry. |
Erections occur spontaneously or by masturbation. Tight circumcision produces a much shorter shaft that is horizontal when flaccid. |
![]() |
50 - 60 mm | If elective circumcision is chosen on parental initiative, it is best done no later than Tanner Stage 1. |
| Mean age (and 'normal' range) at stage boundary:  11.5 (9.5 to 13.5) years | |||||
| Stage 2 | 6 ml Fertility normally begins during this stage. |
First discernible increase in both length and girth. The erect penis may carry at a very high angle, almost touching the abdomen. | ![]() |
50 - 60 mm | First growth of pubic hair that is evidently different from other body hair. Occasional ejaculation now becomes possible by masturbation. |
| Mean age (and 'normal' range) at stage boundary:  12.4 (10.1 to 14.6) years | |||||
| Stage 3 | 14 ml Fertile. |
Growth continues in both length and girth, partly recovering any shortening that resulted from tight circumcision before puberty. | ![]() |
70 - 80 mm | Voice breaks. Ejaculation occurs more frequently in wet dreams or by masturbation. This is beneficial in terms of long-term prostate health. |
| Mean age (and 'normal' range) at stage boundary:  14.0 (11.5 to 16.5) years | |||||
| Stage 4 | 20 ml Fertile. |
-- Ditto -- | ![]() |
Peaks circa 100 mm | Voice matures. Underarm hair develops. Wet dreams frequent in the absence of other sexual activity. |
| Mean age (and 'normal' range) at stage boundary:  16.5 (14.5 to 18.5) years | |||||
| Stage 5 | 28 ml Modern society tends to defer fatherhood to a later age, but in biological terms this is the lifetime peak of fertility. |
Mature size in terms of both length and girth (flaccid and erect) is reached typically five years after crossing the Stage 1 - Stage 2 boundary. | ![]() |
Growth ceases typically six years after crossing the Stage 1 - Stage 2 boundary. | Adult pubic hair distribution. General adult physique and sexuality. |
- Artwork credit: J. Geoff Malta, MA, EdM
- Parents wishing to convey the above information to boys approaching puberty will find a simplified, more child-oriented version here: http://www.puberty101.com. The same website also gives age-appropriate information about puberty in girls.
- Age boundaries have been adjusted from Tanner's original (1960s) work to account for a modern tendency towards earlier puberty. The reasons for this trend are not fully understood.