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Deeper look at ELO: chess rating system E-mail
Written by Yury Markushin   
Friday, 11 February 2011 00:40

lens with eloI already talked about the subject of elo rating but decided to expend previous article with more information and some technical details about elo. This article is not recommended for people who take statistics/predictions way too seriously since this information can ruin their chess results. So read it at your own risk!

The ELO chess rating system is a method of estimating the strength of two players. ELO system isn’t an IQ score. ELO rating does not show how smart you are, how well your memory is, how fast can you calculate chess variations or recognize chess patterns (it is a topic of a separate discussion, how well the IQ score reflects all of the above).

What ELO rating does predict is the result of the game between two players with known ELO ratings.  How it does it? ELO method is based on a precise mathematical equation:

new rating = old rating + K×(W-We).  Where

K-factor is a coefficient which is equal to 25 for new players, 15 for players rated below 15 and 10 for players rated above 2400.

W – Actual score is being calculated by adding 1 for a win, 0.5 for a draw and 0 for a lose.

We- excepted result is based on the fact that the player whose ELO is 100 points higher than the opponent’s ELO wins 64% of the games.

The following table is an approximate version of the winning/losing chances for two players of different strength, based on the formula above. For example if the rating difference between two players is 0 points, meaning that the ratings are the same, each player will score 50% if they play enough games. If one player is 200 points higher rated than his opponent he is expected to win 76% of the games. We can see that according to that statistics 500 points difference means that devastating 96% of the games will be won by the stronger side.

Rating Difference
Expected Result
for a player with higher ELO
Expected result
for a player with lower ELO
0
50%
50%
25
53%
47%
50
57%
43%
100
64%
36%
150
70%
30%
200
76%
24%
250
81%
19%
300
85%
15%
350
89%
11%
400
92%
8%
450
94%
6%
500
96%
4%
735
99%
1%
>735
100%
0%

Even though according to ELO system 2200 rated player 1 is stronger than 1900 rated player 2, it does not automatically means that player 1 will win the game. Player 2 can win and in this case the weaker players rating will increase while the stronger player's rating will go down.

Who uses ELO rating system? Well almost everyone today, starting from FIDE and USCF and ending with online chess servers. 

FIDE has its own gradation of the chess players based on ELO ratings. Here is an approximate table:

  • >2,700 - Grandmaster qualifying for the world championship match
  • 2,500-2,700 - Grandmaster (GM)
  • 2,400-2,499 - International Master (IM) or Senior Master
  • 2,200-2,399 - National Master (NM)
  • 2,000-2,199 - Expert or Candidate Master
  • 1,800-1,999 - Class A
  • 1,600-1,799 - Class B
  • 1,400-1,599 - Class C
  • 1,200-1,399 - Strong Beginner
  • 1,000-1,199 - Beginner
  • <1,000 - New player
  • 100 - Minimal possible ELO rating

In order to obtain a FIDE norm of Grandmaster (GM) or International Master (IM) the following conditions must be true:

1. A minimum of 9 games should be played

2. At least 50% of opponents must be titled players

3. The players score must be equal or higher than minimum performance rating needed for the norm (2600  -   GM norm, 2450 - IM norm).

4. For GM norm at least 30% of the players played must be GMs

5. For IM norm at least 30% of the players played must be IMs. In order to achieve a National Master (NM) norm, it's only needed to obtain a certain rating (2300).

Even though an ELO rating can give more or less reasonable prediction of the game’s outcome based on ratings of the opponents, it does not mean that a weaker player should use this table to see that his chances are nearly equal zero and give up without battle. I hope my readers are not these kinds of chess players.  For those unsatisfied with 3.2 % winning chances I strongly recommend learning how to beat a stronger player at chess and chess self-improvement guide.


Last Updated on Friday, 11 February 2011 00:45
 

Comments  

 
+2 #7 Yury 2011-08-06 00:19
You are welcome. FIDE uses something like the following formula:
Performance rating = [(Total of opponents' ratings + 400 * (Wins - Losses)) / Games].
If you need to get more about the ratings check out the FIDE website: fide.com/.../...
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+1 #6 Swati 2011-08-04 04:03
I also want to know what is the regular formula used by FIDE to calculate my rating.
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+2 #5 Swati 2011-08-04 03:34
Thank you very much for your replies.
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+1 #4 Yury 2011-08-03 23:32
No, I do not think there is a time limit. Until you play these 9 games you count as "provisional" player and have provisional rating. After playing 9 games you turn to "regular" player. FIDE starts using regular formula to calculate you rating after 9 games. Until then, you can gain points quickly or lose it quickly.
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0 #3 Swati 2011-08-02 04:07
Please let me know the time duration during which i have to finish or complete playing these 9 FIDE rated players.
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+1 #2 Yury 2011-07-31 19:43
I believe you need to play at least 9 games again a FIDE rated opponent to get a FIDE rating.
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0 #1 Swati 2011-07-31 08:21
I got a provisional rating of 1635, a year back. For which I played 6 established rated players, out of which I won 2 games, lost 3 games and drew 1 game.I haven't played any international chess tourney since then. How many more rated players do i have to play to get an established rating and what is the time period during which i have to play this game so that i get my rating.
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