It’s important to understand that the size of your penis is determined by genetic traits that are inherited by your parents– similar to your height, eye color, and skin tone. Research studies that have been done list the average adult penis size as about 5 and 6 inches when fully erect, as measured from the lowest portion of the stomach, just above the base of the penis, to the tip of the penis. However, these measurements were taken after puberty when a male has fully developed. Comparing yourself now to other guys, who may have gone through puberty earlier, may lead you to believe that your penis is smaller than others when in fact your body is still developing. When guys hit puberty, a number of changes occur in the body including increased hair growth on certain parts of their body (chest, pubic area, legs, and underarms) and a deepening of the voice. Puberty will also be marked by an increase in the size of your testicles, followed by growth in the size of your penis. The penis typically reaches its final size 4 to 6 years after the testicles enlarge. On average, young men will experience the most rapid growth of their penis and testicles between the ages of 12-16 years. Be patient – guys who develop later than their male friends will eventually catch up to the rest of the pack. Most guys are fully developed between the ages of 18 and 21.