How chess Elo works and what a 200-point gap really predicts
I got my first over-the-board tournament rating (1420) three years ago. Then I got obsessed with what the number actually predicts. Elo turns out to be a beautifully-designed probability system dressed up as a leaderboard, and once you understand the math the whole rating world feels different.
Arpad Elo (Hungarian-American physicist) designed the rating system for the US Chess Federation in the 1960s. It's a relative rating: my 1420 doesn't mean anything absolute, it means I'm expected to score a certain fraction against other rated players. FIDE, USCF, chess.com, and Lichess all use variants of the same math.
The formula
Expected score of player A vs player B: E_A = 1 / (1 + 10^((R_B - R_A)/400)). So a 200-point rating gap: E = 1 / (1 + 10^(200/400)) = 1 / (1 + 3.16) = 0.24 for the lower-rated player. The higher-rated player scores 76% on average (a mix of wins, losses, and draws averaging to 0.76 points per game).
Key gaps to memorize
0 points apart: 50/50. 100 apart: 64/36. 200 apart: 76/24. 400 apart: 91/9. 800 apart: 99/1. Note the log scale — 400 points is a factor-of-10 skill gap in odds. A 2400 GM vs a 1600 player is a mismatch on the order of a professional tennis player vs a good club player.
Rating pools don't match
chess.com Rapid, chess.com Blitz, FIDE Standard, USCF Standard, Lichess Blitz — all different pools with different distributions. Someone rated 1800 chess.com blitz is not the same strength as 1800 FIDE standard (FIDE is much stronger). Roughly: FIDE + 300 ≈ chess.com blitz + 100 ≈ Lichess blitz, but this varies by rating band.
Recap
Elo is a logarithmic probability system. 200 points = 76/24 odds. Rating pools are not comparable; use the same pool to track improvement.
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FAQ
What's Glicko?+
An improved system used by Lichess and others. Adds a 'rating deviation' measuring how confident the rating is. New accounts have huge deviations that shrink with games played.
Can you gain 200 points fast?+
Yes — a strong player entering a new pool at a provisional rating will jump 200-400 points in their first 20 rated games until the system finds their level.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-23 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.