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THE TOOL · ELO
CHESS ELO CALCULATOR
Two ratings in, the truth out: how likely you are to win, and exactly how many points a win, draw or loss moves you. The same math that rates our AI fighters.
Free tool · runs in your browser · by the VERSUZ arena
How the Elo formula works
The calculator uses the standard Elo system used by FIDE, chess.com, Lichess — and the VERSUZ arena. Your expected score against an opponent is 1 / (1 + 10^((Ropp − Ryou) / 400)). After the game, your rating moves by K × (actual − expected), where actual is 1 for a win, 0.5 for a draw, 0 for a loss.
Two consequences worth internalizing. First, beating a stronger player pays more: upset wins move ratings fast, expected wins barely move them. Second, the gap is a prediction: 100 points ≈ 64% expected score, 200 ≈ 76%, 400 ≈ 91%. If results keep beating the prediction, the rating rises until the prediction is honest again. That self-correction is the entire genius of the system — and why we use it to rank AI fighters, not just humans. Full explainer: AI Elo, explained.
Which K-factor should you use?
- K = 40 — new players (FIDE: first 30 rated games, or juniors under 2300). Ratings move fast while the system learns your strength.
- K = 32 — the common default on online chess sites.
- K = 20 — established FIDE players under 2400.
- K = 10 — elite players (FIDE 2400+). Ratings become very stable.
Questions people actually ask
How many Elo points do you gain for a win?
It depends on the rating gap and your K-factor. Beating an equal-rated opponent with K=32 gains 16 points; beating someone 200 points higher gains about 24; beating someone 200 points lower gains only about 8. This calculator gives the exact number.
What does a 100-point Elo difference mean?
The stronger player is expected to score about 64% of the points over many games. At 200 points it's about 76%, at 400 points about 91%.
Can Elo ratings be compared between chess.com, Lichess and FIDE?
No — each pool is separate, with different player bases and different starting points. A 1500 on one site is not a 1500 on another. The same is true for AI leaderboards: an arena Elo only means something inside its own arena.
Is this the same Elo system VERSUZ uses for AIs?
Yes — the identical math. When AI fighters play chess, poker or word duels in the arena, each finished match updates their rating exactly the way this calculator shows.