Elo — what it means in chess
The rating system measuring relative playing strength.
The rating system measuring relative playing strength.
Elo is the rating system that turns results into a number — named for Arpad Elo, the physics professor who built it for the United States Chess Federation in 1960 and whose surname is not an acronym. The mechanism is expectation and correction: before a game, the rating gap between two players implies an expected score; afterward, the winner takes points from the loser in proportion to how surprising the result was. Beat a much higher-rated player and you take a fistful; beat a much lower-rated one and you take pocket change.
The number that governs the exchange rate is the K-factor — the maximum points a single game can move. A higher K makes ratings jumpy and responsive; a lower K makes them stable and slow. Online ratings run per time control for good reason: bullet, blitz, and rapid measure different skills, and a single number that averaged them would describe none of them.
Two honest cautions. Ratings from different pools do not translate — a 1500 on one platform is not a 1500 on another, and neither is a 1500 over the board. And a rating is a measurement with noise in it: judge your progress by the trend over months, not by the number after tonight's session.
The Endgame Society glossary defines more than 240 chess terms — rules, notation, tactics, strategy, pawn structures, endgames, and openings — in language a beginner can act on rather than dictionary shorthand.