Dan is the basic unit of rank used to denote Go strength in the case of professionals and stronger amateurs, dan can be translated as "degree" and corresponds to black belts in martial arts. (Weaker amateurs use the separate kyu system, kyu can be translated as "class" and corresponds to coloured belts in martial arts.) Contrast this with rating, which refers to a more fine-grained, numerical score used to measure Go strength.
Amateur dan levels range from 1-dan (shodan) to 7-dan.
For amateur players, the difference in dan level, often referred to as e.g. four stones stronger, determines the proper handicap. For example, a 5-dan might give a 1-dan four stones. This should produce an even game.
"1d", "2d" and so on is a notation sometimes seen for amateur dan levels.
Amateur dan rankings can be assigned in a number of ways.
- Informal. If you can play even against a 1-dan at your local Go club, you are probably a 1-dan too.
- Ratings-based. Rating systems typically include a mapping to dan levels. For instance, an AGA rating of 3.782 is considered 3-dan. On-line servers have rating systems which map to dan levels as well. In either case, the results may be very high dan levels (8, 9, 10 or even higher) not normally seen in the case of amateurs.
- Awarded by teacher or organization. A professional teacher may award dan rankings informally or formally (amateur dan diplomas) to his or her students, possibly under the aegis of his or her national organization, and national organizations such as the Nihon Kiin award diplomas, sometimes based on rating tournaments.
- Honorary. Honorary ranks may be awarded, such as the 8-dan rank conferred on the winner of the World Amateur Go Championship, or for service to the Go community.
- Self-awarded. Strong amateurs of modest inclination may choose to call themselves 5-dan or 6-dan, even if their actual strength is several stones above that.
There is no uniform international standard for dan levels; they differ by locale , underlying rating system, or even individual Go club. Some systems may be two or even more stones stronger than others. A particular dan system may also exhibit drift over time. For instance, dan rankings in Japan have risen as much as two or three stones since the war--so-called "dan inflation". See RankWorldwideComparison.
The professional dan system is distinct from that for amateurs, ranging from 1-dan (entry-level) to 9-dan. As a rough rule of thumb, the difference between professional dan levels corresponds to one-third or one-fourth handicap stone, and the strength of a typical professional will correspond to that of an amateur 9-dan (if it existed) or higher.
"1p", "2p" and so on is a notation sometimes seen for professional dan rankings.
Professional dan rankings are normally awarded by national go organizations, each with different rules for promotion. Levels may therefore differ somewhat from country to country. They also may differ from actual strength for a number of reasons, including promotion not keeping up with actual gains in strength, or the fact that professionals never go down in dan level, even if they should grow weaker.
One often hears Chinese and Japanese terms used for dan ranks. They share the same characters and are presented in the table below:
|Chinese/Japanese characters||Chinese Hanyu Pinyin||Japanese rōmaji||Meaning||Remarks|
|一段 / 初段||yīduān / chūduān||ichidan* / shodan||1-dan||* The Japanese prefer to use 初段 (shodan) over 一段 (ichidan).|
|十段*||shíduān||judan||10-dan||* 十段 (shíduān, judan), is not a rank per se, but the name of a tournament as well as the honorary title given to its winner.|
The word dan can be used in general to refer to players at any amateur dan level (dan player), problems suited to a dan level (dan-level problem), a weaker player who plays well against stronger ones (dan killer), and so on.
The dan system used in go is basically the same system as used in the Japanese martial arts.
 Bob McGuigan: I question the use of "honorary" for ranks awarded to winners of major amateur tournaments such as the WAGC. The Nihon Kiin also gives 8-dan diplomas to winners of the Amateur Honinbo and other national championship tournaments. Winning such a tournament is a very strong indication of go strength, actually probably professional level go strength. The professional go associations award promotions to real ranks for winning tournaments, why not do the same for amateurs?
 Monteo 2D, Traditional ranking counts the newbies in go as 30 kyu in rank. Modern ranking counts the best player of the time as 9 dan. Hence, the 9 dan champion of this year may be weaker or stronger than the 9 dan champions of other years. That's why the best 9 dan player in one country is weaker or stronger than that in another country.