The good news is that penis size is rarely a medical problem. The bad news is that there are few answers about "normal" penis size that will satisfy a curious teenage boy. There always seems to be pressure to be bigger and larger, and boys always think that they are smaller than average.
A teen boy's genitalia (penis and scrotum) develop in somewhat predictable stages. A boy's scrotum won't begin to enlarge until he is at least 9 years old. A penis can sometimes begin to lengthen at around 9 years old, but won't usually begin to lengthen until 10 years old. If your son is concerned that his penis hasn't started to grow yet -- don't worry. Sometimes a penis won't begin to get longer until the teen is 14 years old. If there is no change by the time he is 14 years old, a trip to the doctor may be necessary. Your pediatrician or family healthcare provider can let you know if your son's development is normal or not.
Puberty and penis size: Length by age.
These lengths are taken from a table in the textbook Adolescent Health Care: A Practical Guide. These are approximate ranges of nonerect (soft) penises.
- Age 10 to 11: 1.6 inches (4 cm) to 3.1 inches (8 cm)
- Age 12: 2.0 inches (5 cm) to 4.0 inches (10 cm)
- Age 13: 2.0 inches (5 cm) to 4.7 inches (12 cm)
- Age 14: 2.4 inches (6 cm) to 5.5 inches (14 cm)
- Age 15: 3.1 inches (8 cm) to 5.9 inches (15 cm)
- Age 16: 3.9 inches (10 cm) to 5.9 inches (15 cm)
- Age 17: 3.9 inches (10 cm) to 6.3 inches (16 cm)
- Age 18: 4.3 inches (11 cm) to 6.7 inches (17 cm)
A 2007 study from Brazil listed the average penis lengths of Brazilian teens. They measured what they called the "real fully-stretched flaccid length," meaning that the penis was soft (not erect) but stretched to be close to the length of an erect penis. The penis was measured by pressing the fat down at the base of the penis and taking the measurement from there (very close to the body) to the tip of the penis. This was also done on the "dorsal" side of the penis, which is the underside of the penis that lies closest to the body when standing. What does all of this mean? It means that measuring penis size is a tricky thing, and is affected by many different factors. Unless you are measuring the penis the same way a researcher did it, it can cause a lot of confusion, so take these numbers with a grain of salt. Your son may be measuring himself in a way very different from how a researcher does it, so these numbers are only a guide.
- Age 10: 2.9 inches (7.4 cm)
- Age 11: 3.1 inches (7.8 cm)
- Age 12: 3.4 inches (8.6 cm)
- Age 13: 4.0 inches (10.1 cm)
- Age 14: 4.5 inches (11.5 cm)
- Age 15: 5.1 inches (12.9 cm)
- Age 16: 5.2 inches (13.3 cm)
- Age 17: 5.6 inches (14.3 cm)
- Age 18: 5.7 inches (14.5 cm)
These numbers reflect the average penis size based on their study in Brazil. Normal size can range from approximately 1 inch to 1.5 inches larger or smaller than these averages. Because the studies haven't been done, it's impossible to know if these size ranges reflect teen boys in other countries, but I suspect the numbers wouldn't be drastically different.
As always, if there is a question or concern about your son's body or development, contact your pediatrician. Again, penis size is rarely a medical concern. Your job as a parent is to reassure your son that he is growing and developing normally and that his body is fine just the way it is.
Gabrich, P.N., Vasconcelos, J.S.P., Damiao, R., and da Silva, D.A. Penile anthropometry in Brazilian children and adolescents. Jornal de Pediatria (Rio J) 2007;83(5):441-446.
Neinstein, LS. Adolescent Health Care: A Practical Guide, 2002.