What are blank tiles for in mahjong?
Officially, nothing: blank tiles are not part of the National Mah Jongg League rules. Some groups play a house rule where you may trade a blank for a discard already on the table. If your group uses blanks, agree on the exact rule before you play.
Not in the official game
A standard American game uses 152 tiles. Blanks are extras that some sets include.
The common house rule
A player puts a blank in the discards and takes a tile of their choice from the discards instead. Groups differ on when this is allowed.
Agree first
Decide whether blanks are in, and exactly how they work, before the first deal.
Common questions
Are blank tiles the same as jokers?
No. Jokers are wild in groups of three or more. Blanks only matter if your group plays a blank house rule.
Should I remove the blanks from my set?
If your group doesn't use them, set them aside before you shuffle so everyone plays with exactly 152 tiles.
Can blanks replace a lost tile?
Yes. Many players keep blanks as spares to mark in for a missing tile.