Well, that's probably average for a center stone, generally, but there are other considerations . . . the four c's
cut color clarity carat
So, if you have a one carat that is flawless and a unique cut, you have a stone that is 'worth' much more than a 2 carat with flaws (which, by the way, the naked eye CANNOT see), etc., etc.
I put 'worth' in quotes because all that matters is that the ring means he wants to be with you forever, and everyone who sees your finger knows it!!!! I happened to have the accidental luxury of picking my own ring, because we happened to be in the store for something else and both loved the same ring, but when I look at it, I don't feel the same feeling as when I looked in the case:
Then, I looked and said 'oh my god, i love that ring' Now, I look and say 'oh my god, I love that Man'