if i am 1777 rated in chess.com what would b my FIDE rating
As a rule of thumb Subtract about 200 points from your correspondence rating and about 100 from your live rating.
what is thumb subtract
Skip the "thumb" part. You're probably safe if you subtract 300 points from your present 1777 rating. So, you're close to being rated 1500 elo.
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if i am 1777 rated in chess.com what would b my FIDE rating