OVERVIEW
Battle.net maintains both a win/loss record and a rating for each player who plays in ladder games. Players gain rating points for each win, and lose rating points for each loss. Because ratings take into account not only the number of wins and losses but also the skill of each opponent, they are a useful measure of the true skill level of a player.
The rating system used by Battle.net is the same Elo rating system that used in competitive chess, golf, and tennis. The Elo rating is a scientific model which provides a meaningful way to compare the skill level of different players, based on the assumption that skill levels follow a normal bell curve.
This web page provides an overview of how the rating system works, and how Battle.net maintains its ladders.
LADDER GAMES
Only ladder games count towards your rating and ladder standing. To create or join a ladder game, select the "Ladder Game" option from the list of game types. You must accumulate at least ten non-ladder wins to be eligible to create or join ladder games.
Ladder games do not allow teams, allies, or shared vision. Ladder games also have the game speed fixed at the "fast" setting.
Ladder games which last less than five minutes are not counted towards your record, rating, or rank.
PROBABILITY OF WINNING
Battle.net computes the probability of each player winning a ladder game based on that player's rating and the ratings of each of the players he is playing against. This probability is used to determine how many rating points the player wins or loses for winning or losing the game. A player who wins against a much higher rated player will gain many points for the victory, while a player who wins against a much lower rated player will gain very few points.
For two player games, the following formula is used to compute the probability of winning:
Probability = 1 / (1 + 10^(-difference_in_ratings / 400))
You can use the following charts to quickly estimate your probability of winning against another opponent:
When playing a HIGHER rated player:
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When playing a LOWER rated player:
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Rating Difference
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Probability of Winning
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Rating Difference
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Probability of Winning
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400
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9.1%
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0
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50%
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350
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11.8%
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50
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57.1%
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300
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15.1%
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100
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64%
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250
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19.2%
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150
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70.3%
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200
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24%
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200
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76%
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150
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29.7%
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250
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80.8%
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100
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36%
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300
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84.9%
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50
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42%
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350
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88.2%
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0
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50%
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400
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90.9%
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When more than two players participate in a ladder game, probabilities are adjusted downward accordingly. For example, in a three player game, each player's probability of winning is divided by 3/2.
DEVELOPMENT COEFFICIENT
Each player is assigned a development coefficient (K), which determines the maximum number of rating points that can be won or lost in any one game. The development coefficient starts at 25 and then drops lower as the player becomes more experienced. This enables new players to move quickly towards a rating that reflects their true ability level, while adding a level of stability to the ratings of more experienced players.
The development coefficient is calculated according to the following rules:
- K=25 for new players
- K=15 for players who have played 30 or more ladder games
- K=10 for players who have attained a rating of 2400 or higher (even if their rating later dropped below 2400)
RATING CHANGE
Each player who completes a ladder game wins or loses points according to the following formulas:
- Winner's rating increases by K * (100% - probability_of_winning)
- Loser's rating decreases by K * probability_of_winning
Players who are disconnected a ladder game prior to the completion of the game do not gain or lose any rating points. However, they gain one disconnect. Because it is possible that some players may intentionally disconnect their system from the Internet rather than take a loss, you should be wary of playing against any players who have a high number of disconnects.
Battle.net does not award any rating changes for a ladder game unless there was at least one winner and at least one loser, and the game lasted at least five minutes. Also, if any winner gains one or more rating points, Battle.net ensures that each loser loses at least one rating point, even if their probability of winning was so low that the computed rating adjustment rounds to down zero.
LADDER
The top 1000 rated players in the world are given official rankings on the Starcraft ladder. Ladder rankings are recomputed every night at midnight Pacific time.
Ladder games which include one or more ranked player are automatically reported to the Ladder Games forum. In order to keep the volume of posts reasonable, ladder games which do not include any player in the top 1000 are not posted.
Each ladder lasts for three months. At the end of a three month season, Blizzard declares a world champion for that season, and resets the ladder and all ratings. The world champion is the person who was ranked #1 at midnight on the last day of the season. The seasons are as follows:
- Winter Ladder Dec 1 - Feb 28/29
- Spring Ladder Mar 1 - May 31
- Summer Ladder Jun 1 - Aug 31
- Fall Ladder Sep 1 - Nov 30
REPORTING ABUSES
It is considered an abuse of the ladder system to:
- Repeadly play the same opponent(s),
- Intentionally lose to an opponent to increase his rating, or
- Disconnect from a game for the purpose of avoiding a loss.
Because the results of all ladder games between ranked players are posted to the Ladder Games forum, any interested observer can easily check the record of a ranked player to see if he is repeatedly playing against the same opponents or repeatedly disconnecting from games.
Please report all suspected abuses of the ladder to "support@blizzard.com". Include as much information as possible documenting the pattern of abuse. Blizzard may, at our sole discretion, delete the Battle.net account of any player suspected of abusing or attempting to abuse the ladder system.
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