In short: A rating system that measures playing strength with a number. The higher the number, the stronger the player.
Also called Elo rating.
The Elo system was developed by Arpad Elo, a Hungarian-American physics professor and chess master. The International Chess Federation, FIDE, began using it in 1970, and today FIDE calculates Elo ratings for players all over the world. Since Elo is a name, it isn't written ELO.
How it works
The idea is simple. The difference between two players' ratings predicts how the game should go. After the game, the result is compared with the expectation. If it went better than expected, your rating goes up; if it went worse, it goes down. Beat someone much stronger and you gain a lot of points. Beat someone much weaker and you gain only a few.
| Rating difference | Expected share of the points for the stronger player |
|---|---|
| 0 | about 50 percent |
| 100 | about 64 percent |
| 200 | about 76 percent |
| 300 | about 85 percent |
| 400 | about 91 percent |
The change is calculated as K × (result − expected result), where the result is 1 for a win, ½ for a draw and 0 for a loss. K is a number FIDE sets. It is higher for new and young players, so that their ratings quickly find the right level.
Ratings online
Chess sites have their own rating systems, often built on the same idea but with other formulas and completely different players. So the numbers can't be compared directly, neither with each other nor with FIDE's.
Titles
FIDE's titles are partly tied to the rating. The highest, grandmaster, was first awarded in 1950. To become a grandmaster you need both a high rating and strong results in several tournaments.
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Frequently asked questions
Why is it called Elo?
After Arpad Elo, a Hungarian-American physics professor and chess master who developed the system. FIDE began using it in 1970. So Elo is a name, not an abbreviation, and isn't written in capitals.
Is an online rating the same as a FIDE rating?
No. Chess sites calculate with their own systems and their own players, and their numbers can't be compared directly with FIDE's.
What does a 200-point difference mean?
By Elo's formula, the stronger player is expected to score about 76 percent, roughly three points out of four.
Updated October 31, 2026