This type of question comes up quite a lot and normally ends up in heated debate. For what its worth, here are some stats which might interest you.
http://www.chess.com/article/view/chesscom-rating-comparisons
Chess.com Ranking
Sort:
Most Recent
Forum Legend
Following
New Comments
Locked Topic
Pinned Topic
How does Chess.com ranking relates to standard Elo / Fide rankings?
Do we have to take away around 150 points?
I have seen some GMs on here whose's chess rankings have discrepancies with their FIDE ranking
Obviously the games they play here may skew the results but what about a ranking of say 1800. what is the equivalent FIDE / Elo ranking?