What is the average penis size?

Answer:

The average length and circumference of a human penis, whether non-erect (flaccid) or erect, depends upon age rather than height, weight, or race.
There is no significant difference between measuring an uncircumcised or circumcised penis when erect as the length is just the same. When a foreskin is covering the glans of the flaccid penis there is a minute difference of around plus .08cm to consider.
(Note: 1" = 2.54 cm)

PENIS LENGTH :
The average length of a flaccid penis for a pre-pubescent boy depends upon age, but you will see that little growth is made during these early years. A baby's penis is 1" (2.5 cm), and a 10-year-old's penis is 2" (5.0 cm). Significant growth begins during puberty which on average starts at 12-years-old. By around 20-years-old, the penis will have reached its full adult size. The average adult-male flaccid penis measures 3.8" (9.5cm).
The average length of an erect penis by age in inches and cm's:
12 yrs: 2.3" (5.8 cm)
13 yrs: 3.4" (8.6 cm)
14 yrs: 3.9" (9.9 cm)
15 yrs: 5.1" (12.8 cm)
16 yrs: 5.4'' (13.6 cm)
17 yrs: 5.7" (14.5 cm)
18 yrs: 5.9" (15.0 cm)
19 yrs: 6.0" (15.2 cm)
20 yrs and over: 6.1" (15.5 cm)

To accurately measure the length of your flaccid or erect penis, place a ruler or tape measure along the top of your penis, where it joins the abdomen, and measure to the tip of the glans.

PENIS CIRCUMFERENCE :
The average circumference of the adult-male organ measures 3.93" (10cm) when flaccid and 4.92" (12.5 cm) when erect.
The average circumference of an erect penis by age in inches and cm's:
12 yrs: 2.5'' (6.3 cm)
13 yrs: 2.9'' (7.6 cm)
14 yrs: 3.4'' (8.6 cm)
15 yrs: 4.0'' (10.1 cm)
16 yrs: 4.2'' (10.6 cm)
17 yrs: 4.4'' (11.1 cm)
18 yrs: 4.6'' (11.6 cm)
19 yrs: 4.8'' (12.2 cm)
20 yrs and over: 4.9'' (12.5 cm)
To accurately measure the circumference of your flaccid or erect penis, place the tape measure midway along the length, and loop it around.