Rating calculation formula
Rdiff = K*(Sa-Se)
Rdiff – rating difference for single game
K – K factor (depends on type of rating: established or provisional, see below)
Sa – actual score (0 for loss, 1 for win and 0.5 for draw)
Se – expected score (see formula below)
The expected score is calculated as following:
Se = 1/(1+10^((R2-R1)/400))
R1 – is player’s rating (player whose rating is calculated)
R2 – is opponent’s rating
Established and Provisional ratings
If the player has 10 or more games against Established players and gained 3 points from Established players, then such player has Established rating.
Other players have Provisional rating.
Provisional rating is calculated by formula: Rp = Ra + 400*(W-L)/N
Ra – average rating of established opponents
W – number of wins
L – number of losses
N – number of games (all versus established)
K factor.
K factor is a coefficient which defines maximum rating deviation from player’s game result.
For Established player playing versus another Established player the K factor = 32

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