2 inches
5cm
Some people will some people won't (most people won't). If you're still young (teenager), then the best way to get a bigger penis is to masturbate. But if you're older (18+), about the only way is...
Eat well,get at least 8 hours of sleep and simply go though puberty. you'll be fine.
Jonah Falcon currently holds the record at 13.5 inches.
about 6.5 in