Go ranks and ratings

Skill in the traditional board game Go is measured by a number of different national, regional and online ranking and rating systems. Traditionally, go rankings have been measured using a system of dan and kyu ranks. Especially in amateur play, these ranks facilitate the handicapping system, with a difference of one rank roughly corresponding to one free move at the beginning of the game. This system is also commonly used in many oriental martial arts, where it often corresponds with a belt color. With the ready availability of calculators and computers, rating systems have been introduced. In such systems, a rating is rigorously calculated on the basis of game results.

Traditionally, the level of players has been defined using kyu and dan ranks. Kyu ranks are considered student ranks. Dan ranks are considered master ranks. Beginners who have just learned the rules of the game are usually around 30th kyu. As they progress, they advance numerically downwards through the kyu grades. The best kyu grade attainable is therefore 1st kyu. If players progress beyond 1st kyu, they will receive the rank of 1st dan, and from thereon will move numerically upwards through the dan ranks. In martial arts, 1st dan is the equivalent of a black belt. The very best players may achieve a professional dan rank.

The rank system is tabulated from the lowest to highest ranks:

Although almost all organizations use this system, there is no universal calibration. The means of awarding each of those ranks and the corresponding levels of strength vary from country to country and among online go servers. This means that a player who is considered to be a 2nd kyu in one country, may only be considered a 5th kyu in another.

Differences in strength up to amateur dan level generally correspond to the level of handicap that would yield an even game between the two players. For instance, it is expected that a 3d player could give 2 handicap stones to a 1d player and win half of his or her games. In contrast, differences in professional ranks are much smaller, perhaps 1/4 to 1/3 of a handicap stone. There some significant differences in strength between ordinary 9p players and the best players in the world because 9p is the highest rank possible, which may account for this variation.

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Wikipedia