Short answer

Penis size varies a lot from person to person. Many males reach an average adult erect length of about 13 cm (5.1 inches), but there is a wide normal range. At 16, your penis may still change in size as you finish puberty — growth often continues into the late teens or early 20s.

Step-by-step explanation

  • Variation is normal: Genetics, body fat, and the timing of puberty all affect size. Two people the same age can look very different and both be completely normal.
  • Average numbers (for adults): Large studies report an average erect length around 13 cm (5.1 in), with many adult men shorter or longer than that. For teenagers the situation is more variable because development is ongoing.
  • Growth timeline: Penis growth usually happens during puberty along with testicular growth, voice changes, and body hair. For many people this starts between about 9–14 years and continues for several years. Some growth can continue into the late teens or early 20s.
  • How doctors measure size (medical context): Length is typically measured along the top from the pubic bone (pressed gently to the bone to account for fat) to the tip of the penis. Circumference (girth) is measured around the thickest part. These measurements are used in medical settings, not to compare socially.
  • What affects apparent size: Body fat at the pubic area, weight changes, temperature, and whether you are flaccid or erect can change how large the penis looks. Flaccid size is not a reliable indicator of erect size.
  • Size doesn’t define health or ability: Penis length does not determine fertility, sexual performance, or your worth. Many worries come from comparing yourself to unrealistic images online or in pornography.

When to talk to a doctor

See a healthcare provider if you have any of the following concerns:

  • Your penis seems extremely small compared with peers and you’re worried (a doctor can assess growth and hormone levels).
  • You have severe curvature, pain during erections, trouble urinating, or any other physical problem.
  • You haven’t had any testicular growth or other signs of puberty by about age 14–15 (this can indicate delayed puberty).
  • You feel very distressed or anxious about your body — a doctor or counselor can help with support and information.

Where to get help

  • Talk to a trusted adult (parent, guardian) or your school nurse if you can.
  • Make an appointment with your family doctor, pediatrician, or a clinic that specializes in adolescent medicine or urology.
  • If you prefer confidential advice, look for local sexual health clinics or organizations (for example, in many places there are youth clinics or Planned Parenthood branches).

Final reassurance

Worrying about size at 16 is very common. Most people are within the wide normal range, and many still grow a bit more. If this is causing you anxiety or if you think your development is delayed, a medical visit can give clear, private answers and peace of mind.

Note: This information is educational and not a medical diagnosis. For personalized advice, see a healthcare professional.