It really, really varies from person to person and how seriously they take each type of game.
I take OTB tournament games much, much more seriously than I take chess.com play. My USCF rating is currently five points lower than my online chess rating.
Maybe this question should be posted as a sticky topic at the top of the forum. It seems to get asked pretty often. I even asked it when I first signed up here.
You can come up with some very rough extrapolation but in the end it devolves, at least, to different rating pools.
Different pools, no direct relation.
It'd be like asking to compare sprint times for someone running on Earth and for someone running on Mars.
My chess.com rating is about 200 points BELOW my USCF rating. I think that this tends to be true for most players. Anyone with any type of life has to deal with a bunch of distractions while playing on-line (wife or girlfriend talking to you while you're playing, doorbell, telephone, etc.). These distractions don't occur in tournament play, and I think that most people would have a higher OTB rating as a result.
I'm fairly sure that, for me, when I start playing OTB my rating will be a fair bit lower than the ~1900 I was in online chess before timing out a bunch last year.
My chess.com rating is about 200 points BELOW my USCF rating.
This is the norm (for 'live' timed chess, not 'online' postal chess).
How much do you estimate that the rating differs between OTB rating and chess.com rating in here you have the analysis board and access to database.
So there is more or less no need to know any opening since you can always use game explorer.
I think that chess.com rating can be 300+ OTB rating higher. if you use all tools available that you are aloud to use. maybe even higher since database moves ensures that you do not blunder. however your opponent do not have database moves access OTB which they do on chess.com
please keep this discussion clean , no talk about computer aid. we have a saying in Denmark "thief thinks everyman is stealing"