From Japanese mahjong wiki
Three player essentially plays like the regular four player game but with some changes.
- Chii disabled
- Removal of one suit
- Typically, the manzu suit is removed. Though, the terminals (1-man and 9-man) remain in order to retain the possibility for kokushi musou.
- The dead wall
- The dead wall is arranged differently.
- North tile dora
- By use of kita 「キタ」, possession of the north tile may be put to the side of the hand, like an open call; and it would be counted as dora. Plus, the player is also awarded an extra draw from the dead wall for that north tile.
- If the player wins off of the dead wall draw from calling kita, they are awarded rinshan.
- A kita call can be ronned, but this does not award chankan.
- For scoring, the same scoring table is used. Both ron and tsumo values remain the same. However, for tsumo, no change is used to account and adjust for the missing player. Therefore, the total points for tsumo is less than that of the ron total.
- Sanma in Japanese Wikipedia