How do chess websites ratings compare to real FIDE ratings?

Just curious if there is any table showing how ratings on chess websites like chess.com compare to OTB FIDE ratings? 

https://www.chess.com/blog/smarterchess/chess-rating-comparison-2016

I have a question I'd like to piggyback on top of this one.  Chess.com's computer opponent has ten levels of strength.  Does anyone know what the approximate FIDE rating strength of these levels are?  I can beat level 5 fairly reliably, but level 6 is tough for me unless I really concentrate on avoiding bad moves. 

The computers with the ten levels can't be rated because 1) there is no time control and 2) human takebacks are allowed.

notmtwain, that's why I said "approximate".  Of course they can't be formally rated, but they do have a level of strength analogous to a rating, and I'm curious what they are.