Odd things, daily.
“Micropenis” occurs in about 0.6% of males, and is identified when an erect penis is smaller than 7cm (2.8 inches). The condition is usually recognised shortly after birth, and is often treated with a brief course of testosterone. Whilst this technique induces a small amount of growth, the subject rarely achieves what would be considered “normal size”.
Other micropenis sufferers attempt surgery similar to phalloplasty, where a penis is artificially constructed, but these techniques are rarely considered successful.
The smallest penis ever recorded was 1cm (0.39 inches) when erect.
At the other end of the scale, the living owner of the worlds biggest penis is Brooklyn man Jonah Falcon at 34.3 cm (13.5 inches) erect, pictured below.
Jonah Falcon, worlds biggest penis
I was as surprised as you are.