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Chess Ratings - How They Work

  • erik
  • | Aug 23, 2007
  • | 132714 views
  • | 483 comments

Like it or not, we ALL have a chess rating. You may not care at all about your rating, or you may be whining every time it goes down in the slightest. You might be someone who plays a game a year, or someone who plays 1,000 a day. Still, there is a number out there that represents how well you play chess. Well, that's the theory, anyway.

To understand chess ratings you have to understand two things: #1 - that you have a TRUE rating that perfectly represents your strength of play, and #2 - that that TRUE rating will never be known and so we have to use statistics to get as close as possible to the truth. I'm writing this article in response to many people who ask about ratings and need a simple explanation of how they work. (I only know about all this because of a recent super-in-depth statistics course I took and my research in building Chess.com!)

There are two main rating systems, and each one has its merits.

The Elo System (used by the United States Chess Federation, FIDE, and many other online chess sites) is popular for two reason - it has been around for a long time, and it is simple. The idea is this: given two chess players of different strengths, we should be able to calculate the % chance that the better player will win the game. For example, Garry Kasparov has ~100% chance of beating my 4-year-old daughter. But he may only have a ~60% chance of beating another Grandmaster. So when playing that other Grandmaster, if he wins 6 games out of 10, his rating would stay the same. If he won 7 or more, it would go up, and 5 of less, his rating would go down. Basically, the wider the spread of the ratings, the higher percentage of games the higher rated player is expected to win. So to calculate a person's rating after playing a few games you calculate the average ratings of his opponents, and then how many games he was expected to win, and then plug it into a formula that spits out the new rating. Simple enough. Well, it turns out, that is maybe TOO simple.

The Glicko System (used by Chess.com, the Australian Chess Federation, and some other online sites) is a more modern approach that builds on some of the concepts above, but uses a more complicated formula. (This only makes sense now that we have computers that can calculate this stuff in the blink of an eye - when Elo created his system they were doing it on paper!) It is a bit trickier than the Elo system, so pay attention. With the Elo system you have to assume that everyone's rating is just as sure as everyone else's rating. So my rating is as accurate as your rating. But that is just not true. For example, if this is your first game on Chess.com and you start at 1200, how do we really know what your rating is? We don't. But if I have played 1,000 games on this site, you would be much more sure that my current rating is accurate. So the Glicko system gives everyone not only a rating, but an "RD", called a Rating Deviation. Basically what that number means is "I AM 95% SURE YOUR RATING IS BETWEEN X and Y." (Nerd Fact: In technical terms this is called a "confidence interval".) If this if your first game on Chess.com I might say, "I am 95% sure that your rating is somewhere between 400 and 2400". Well that is a REALLY big range! And that is represented by a really big RD, or Rating Deviation. If you have played 1,000 games and your rating is currently 1600 I might say "I am 95% sure your rating is between 1550 and 1650". So you would have a low RD. As you play more games, your RD gets lower. To add one extra wrinkle in there, the more recent your games, the lower your RD. Your RD gets bigger over time (because maybe you have gotten better or worse over time - I'm just less sure of what your actual rating is if I haven't seen you play recently). Now, how does this affect ratings? Well, if you have a big RD, then your rating can move up and down more drastically because your rating is less accurate. But if you have a small RD then your rating will move up and down more slowly because your rating is more accurate. The opposite is true for your opponent! If they have a HIGH RD, then your rating will change LESS when you win or lose because their rating is less accurate. But if they have a LOW RD, then your rating will move MORE because their rating is more accurate.

I wish there was some simple analogy to explain all this, but there isn't. It all comes back to this: you have a theoretically exact chess rating at any given moment, but we don't know what that is and so we have to use math to estimate what it is. There are really smart people out there who work on this stuff for a living, and at the end of it all we get to put their proven methods into our code so that we can all enjoy knowing what little numbers next to our name we deserve.

If you want to read more, check out these articles (WARNING - SEVERE NERD CONTENT AHEAD):

- The Glicko System by Professor Mark Glickman, Boston University

- Introduction to Chess Ratings (Elo mostly) on About.com

Comments


  • 2 years ago

    gauravvichare99

    rating doesn,t matter

  • 2 years ago

    ameriken

    It looks like the average is right around 1250-1350 range, you can view the graph on the 'Players' link in the upper right hand corner of your home page.

  • 2 years ago

    Totenbonde

    Another thing (sorry about posting two times): What is the average rating of all players in chess.com? Is it 1200? 

  • 2 years ago

    Totenbonde

    Strange about ratings. I see people with much higher ratings than me having troubles with puzzles I find easy. I myself rate 300 higher in the tactic trainer than on blitz games. Maybe this points out my strengths and weaknesses. Or it may be that some of these peoples ratings are uncertain because of a low number of games played/a high RD, if I understand the article right. But where can this RD be found? 

  • 2 years ago

    Mr_Norm

    Good explanation Eric. I am ranked in the 95 th percentile around 30,000 out of 600,000 standard players and my rating is around 1500+ . Is this because we all started out at 1200 and nobody with a higher rating will play me. I set the search criteria for +400/-400 and I only get players weaker than me or equal.  I never seem to get any of the 5% who are better. I'd like to see a bell shaped curve of all standard players. Thanks again Eric. Please reply. Mr_Norm. 

  • 2 years ago

    anthonyweatherbee

    Bull shit ! when my opponent runs out of time and I have more higher pieces I still lose my rating ! Also there has been times when my opponent has made three move to my one ! the program is flawed and wrong .

  • 2 years ago

    PCL91

    science_man_88   Yes obviously I read it,but my ratings were going slightly strange so the article didnt cover everything to what was going on with my ratings.

  • 2 years ago

    science_man_88

    PCL91  did you read the article ? it's clearly stated in it why this might happen

  • 2 years ago

    PCL91

    I have played about ten online games so far and for example in the rating adjustment if I lose, my rating goes down by sometimes 80 points, that is when I am playing someone who is a lower rating then mine, however my friend has an account on chess.com and when he is playing someone who has a much lower rating then him, in his rating adjustment if he loses his rating would only go down by about 18 points.  Why is this ??? Any answers much appreciated.  Thanks.

  • 2 years ago

    leochap

     Well, I've had some interesting and helpful replies ...Thank you very much all who have contributed. I hope Chess Com does not scoop it all up before I, and others interested,  have had a chance to make some notes. Leochap (He with the lowly rating)

  • 2 years ago

    nyLsel

    @snoopchuck: Your account will only be rated if you play rated games.

  • 2 years ago

    snoopchuck

    Hi, does anyone know how to change an account from an unrated one to a rated one? Thanks a lot! 

  • 2 years ago

    peppapig4

    :( Honestly!!! why they are aborting my game in Blitz :(  they're not even have a high points.

  • 2 years ago

    Ineedphenylalanine

    I do not think it is possible to play 1000 games a day. There are only 1440 minutes per day, and even if each of the games lasts only one minute each, they still have to sleep and eat.

  • 2 years ago

    nigelzub

    the live ratings  r the only ratings that mater  30 mins each side  not two days to move . on line chess is the real  deal 

  • 2 years ago

    frankiebouy

    hi. could any explain why my rating in live chess has never changed and i have been playing along time now. forthy games at least

  • 2 years ago

    worldthought_com

    I like how you said Kasparov has "about" a 100% chance of beating your 4 year-old daughter. 

  • 2 years ago

    emilsonpl

    How does chess.com ratings compare to FIDE ratings?

    It seems that chess.com ratings are shifted down. Is this because players start with 1200 or is it more due to the different math method of rating calculation?

    Regards,

    Emilson

  • 3 years ago

    Sledge290

    I am glad that I rediscovered you! It's been a long time and I have been playing a (little) chess on  Pogo.com. They don't have problems initiating a game when my opponent plays the white pieces. You do, in all due respect. I am waiting for my opponent to make his move with the white pieces. Why haven't you set up things in a working manner here that will notify him that I have started a game using the black pieces, and have to wait for him to make his, i.e. the first move? What is the matter here? Today is February 25, 2012. I await you quite necessary reply, after you repair the problem, please.

  • 3 years ago

    Rafchess

    ssdeep u played with an opponentof lower rating! that's reason for droping down of ur current rating.

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