That's silly criteria, as the length from cock to navel isn't at all consistent from person to person.
Same with hand size, you can have huge hands, the next guy can have small hands and it'll change it drastically.
I am a walking example of how this criteria is incorrect.
My dick is fairly long, but its set lower on my groin than a normal person, so it barely reaches my belly button; however, if my dick were set in the same place as everyone elses, my dick would be well above my belly button.
And my hands are incredibly small but I have a bigger dick than anyone I've ever met with bigger hands than me.
One dude I knew was like six and a half feet tall with giant hands and he had a tiny dick.
I'm not looking down on people for having smaller penises, just saying all of these rules and myths are wrong. Not all of them, but most of them.
And I'm proof that most of these myths are wrong.
{and I've seen proof-negative for the blacks and asian myths}
I forgot to post about the original topic:
I would say anything above 6.5 in length and 4.5 in gith is above average, and since average would be considered medium, anything above that could be considered large.
Personal averages are different though; someone might have fucked nothing but nine inches+ so an 8 could seem small.