In the title I said "511 in inches" for a single reason: Anyone below 5 inches already knows that he is small, and he needs to get bigger. I don't believe a guy with a 4.5 inch penis could honestly say "I'm average" to himself. And anyone above 6 inches already thinks he's the hugest, hung-est guy around. Those who are around 511 in inches are the ones who have to know most about what their size means.
For starters, the average penis size is 6.17 inches. It's funny to hear how guys with 6 inch penises think they're well above average because "the average is 5 inches", whereas the truth is that they are BELOW average.
I Am At 5 Inches - Is It Enough?
Of course, it depends on what it is "enough" for. Studies have shown that 5 inches can be enough (it's the minimum) to give orgasms to women. However, people at 5 inches have to climb a mountain to give women orgasms. They have to do everything right - from foreplay to sexual positions to hitting the "right" spots.
A guy with a, say, 7.5 inch penis has a MUCH easier job. The fact is that a penis that size will easily be able to touch the cervix - which has been proven to be the most powerful orgasm trigger in women, even more so than the clitoris.
How deep the cervix is depends on the woman in question. Shorter women will have them closer to the opening, but if you want to please a woman that is taller than 5' 5", then to touch her cervix you will need a penis in excess of 7 inches.
All in all it's impossible to say "5 inches is enough". Yes, technically it is "enough" but you have to do an enormous work in order to satisfy your partner, while you could enlarge your penis 1-4 inches easily with some exercises and have a much much easier job of pleasing every woman you are with.