Tile efficiency
Tile efficiency refers to the speed of hand development. Having better tile efficiency means that the hand is more likely to complete, and is thus faster on average.
Only one person can win per round, and a hand of any value can win. Therefore, learning how to optimize tile efficiency is important to improving at riichi mahjong. Sometimes, it may not be best to go for the maximum efficiency play (e.g. slowing the hand to go for a yaku), but strong players should know how to reach maximum tile efficiency
Tile categories
Tiles can be grouped into a few basic categories:
Isolated
Isolated tiles, also known as "lone" or "floating" tiles, are those with no neighbors. A tile is isolated when there is no tiles numerically or categorically adjacent. Therefore, they may not be used for tile calls.
These tiles are not very useful, so they are often discarded first. However, an isolated tile may be used to "upgrade" the hand. For example, an isolated 5 can be used to improve the hand's shape. An isolated dora can be used to increase the value of the hand. An isolated yakuhai can be paired and then pon'd.
Taatsu
Taatsu 「塔子」, or "joints"/"shapes", are two tiles that can create a sequence. These resemble the basic wait patterns:
| Type | Ryanmen | Kanchan | Penchan |
|---|---|---|---|
| Incomplete |   |
 |
|
| Complete | /  |
|
|
All else equal, a ryanmen is twice as good as the other joints, because they accept twice as many tiles. Kanchans can be upgraded to ryanmens (e.g. 24-pin, after drawing 5, turns into 45-pin).
Toitsu
Toitsu are pairs. Most hands need 1 pair to win. Pairs can be used to create triplets, though, so having multiple pairs can increase efficiency.
Complex joints
Complex joints are a joint made up of 3 tiles. When the joint is completed, two tiles are used in the group, and the third tile becomes isolated.
| Type | Ryanmen + Pair | Kanchan + Pair | Ryankan |
|---|---|---|---|
| Incomplete | |
|
|
| Complete | / / |
/ |
/
|
Tile acceptance
A hand's shanten measures how far a hand is from tenpai. A hand that is 1-shanten is 1-away from tenpai, a hand in 2-shanten is 2-away from tenpai, and so on.
Ukeire, or tile acceptance, measures how many tiles can be used to reduce a hand's shanten. For example, a hand may have a tile acceptance of 40 tiles, meaning that there are 40 different tiles of tiles that can be drawn to advance the hand.
Note: when measuring tile acceptance in actual games, it is important to note the amount of tiles available to draw. Any tile discarded, used in your hand, used in an opponents call, or in the dora indicators can no longer be drawn, which affects the hand's tile acceptance. For example, a 67-pin ryanmen joint normally has an acceptance of 8 (four 5-pins; four 8-pins). However, if all four 5-pin and three of the 8-pin are discarded, the wait effectively has an acceptance of 1 tile.
Important concepts
Five-block theory
"Five-block theory" states that a standard winning hand has five "blocks" - four groups + one pair. Each joint and sequence in the hand is considered a block. Since pairs can turned into triplets, each pair is also a block. When a hand has 6 blocks, one of them will eventually need to be discarded. Thus, it is good to build hands with 5 blocks in mind (i.e., having 6+ blocks is redundant).
Example of blocks:
can be split into:- (group) + (joint) + (joint) + (complex joint) + pair - 5 blocks
- is an isolated tile which does not add anything to the hand.
To see why 5 blocks is important, look at example 2-shanten hands:
| # Blocks | Hand | Tile acceptance |
|---|---|---|
| Hand with 5 blocks |         
|
    (26 tiles total, not counting the tiles in the hand)
|
| Hand with 6 blocks |  
|
 (28 tiles total)
|
The hand with 6 blocks has a better tile acceptance right now, since it can accept 28 tiles total. (Note: the 5 block hand can accept the same # of types of tile, but since some of the tiles are used in the hand, the acceptance is lower. In this case, 2/4 of the 3-sou tiles are used in the hand, so they can't be drawn again.)
However, once a useful tile is drawn, the hand with 6 blocks has to discard one of the blocks, lowering the efficiency in the future.
Example 1-shanten hands:
| # Blocks | Hand | Draw | Discard | Tile acceptance |
|---|---|---|---|---|
| Hand with 5 blocks | |
|
|
(20 tiles total)
|
|
| ||||
| Hand with 6 blocks | |
|
|
(16 tiles total)
|
|
|
Going from 1-shanten to tenpai is the slowest part of the hand. Therefore, it's better to improve tile efficiency at 1-shanten than 2-shanten - the returns are bigger. In this example, the 5-block hand is 15% worse (24/28 tiles) at 2-shanten, but 25% better (20/16 tiles) at 1-shanten.
For this reason, aiming for 5 blocks is generally better for tile efficiency.
- That being said, having 6 blocks is better than 5 blocks with 2 useless isolated tiles. A 6th block is redundant, but better than useless. When you have excess blocks, you can discard one when:
- You can upgrade one of your joints (e.g. turning a 45 ryanmen joint into a 445 complex joint).
- You enter 1-shanten.
- When discarding the 6th block, discard the weakest block you have (the one that improves tile acceptance the least). For example, if deciding between a penchan and ryanmen, discard the penchan. If you have two blocks of 23-man + 56-man, they have "duplicate acceptance" on the 4-man, so discarding one of those only leads to a loss of 4 tiles of acceptance.
- You may want to keep 6 blocks when aiming for a yaku, such as pinfu or sanshoku.
- Sometimes, there may be multiple different ways to interpret a "block" (e.g. 5568 can be seen as 556 + isolated 8, or 55 + 68).
Yaku
At least one yaku is required to win a hand. Therefore, yaku are certainly a key factor for tile efficiency. Having a yaku means you don't need to riichi for a yaku, which means you can call tiles, which allows you to complete tiles faster than a closed hand would. When you need to complete a fast hand, confirming a yaku is important. Of course, sometimes it's best to stay closed for the value.
In other cases, players may end up simply having tenpai in mind, especially as the hand nears the later discards. This is of particular concern for the current dealer, who may have an interest in retaining the position and repeat the hand.