Why Chess.com rating different from lichess??

If someone's rating is 1800 on Lichess, then how much will be on Chess.som

Did you try searching the forums? therein plenty of this discussion already

In addition to the excellent information provided in the lichess link provided by @glbert , it's worth repeating or emphasizing that the rating refers to your chance of winning against other players IN THE SAME POOL, so even if two different sites use the very same rating system, you cannot extrapolate how well you will perform in one sites pool from your rating in the other sites pool of players.

It is easy to understand. Say both organizations use the Glicko-2 ratings system. An average player on both sites has a rating of 1500 (because of how Glicko-2 is defined). Now imagine if one of those two organizations consisted of only titled players and the other consisted mainly of casual amateur players. Ofcourse someone having a 1500 rating on the title player site would beat most players on the amateur player site. Hence their rating on the amateur player site would end up being much higher than 1500.

I would say around 1500

About 200 points lower, from my experience. So around 1600.

@Hdhshshh said in #1:
> If someone's rating is 1800 on Lichess, then how much will be on Chess.som

1300 or less in rapid. I don't know about faster games.

Impossible to say accurately. Both sites uses different rating algorithms.

@pointlesswindows I highly doubt that, an 1800 blitz player on lichess should never be 1300 rapid on chesscom. I am 1900 blitz on here and 1730 rapid over there.

Lichess is not obligated to sync with chessscom rating system.