On the assumption that this question is not a joke...
Penis size when flacid is irrelevant. Some men have a penis which is very large when flacid, but which changes in size very little when erect. Some men have a very small penis when flacid, which grows substantially when erect, and then others inhabit every possible position in between.
The average size for a penis when erect is between 5 and a half (13.75 cm) and 6 and a half inches (16.25 cm). If your penis is within these measurements, you are entirely normal.
Some men do fall on the extremes. A micro-penis (which is about 1 inch when erect) can be sorted out by surgery. A penis which is very big (and this can be a problem; a vagina is about the same depth as an average penis, so a bigger penis just doesn't go in all the way) cannot easily be reduced in size.
The comedian Richard Herring wrote a very interesting and funny book called 'Talking Cock'. In it, he reports one man writing 'My cock is very big; about six inches'. Another writes, 'I am really depressed - my cock is only about six inches'. That should tell you something important about penis size.
Hope that helps.