What shanten means
A hand that can win with one more tile is tenpai. Shanten counts the steps before that: a 1-shanten hand needs one useful draw to become tenpai, a 2-shanten hand needs two, and so on. A complete winning hand is written as −1. Every step means drawing a tile you need and discarding one you do not, so a lower shanten is always closer to winning, whatever the hand is worth.
Three shapes can win, and the calculator counts each one:
- Sets and a pair: four sets (sequences, triplets or quads) and a pair, the shape almost every hand uses.
- Seven pairs: seven different pairs; in riichi two identical pairs do not count as two (EMA Riichi Rules 2025, 4.2.2).
- Thirteen orphans: one of each terminal and honour plus one more of any of them.
The overall shanten is the lowest of the three. Seven pairs is never more than 6-shanten for 13 tiles, so no hand is ever worse than 6-shanten, even when sets and a pair would need eight steps.
How to choose a discard
With 14 tiles, list every different discard and look at two numbers: the shanten that is left, and how many tiles would improve it next turn (ukeire, "accepting tiles"). Throw the tile that keeps the shanten lowest; among those, the one that leaves the most tiles that help. The calculator sorts the table that way.
The example above: 2-3 characters, 5-6-7 characters, 3-4-4-6 circles, 5-7-9 bamboo and a pair of east winds. It is 2-shanten. Most discards keep it 2-shanten, but they are not equal. Throwing the 6 circles leaves 28 tiles that help in 8 kinds: the 1 or 4 characters for 2-3, the 2, 4 or 5 circles around 3-4-4, the 6 or 8 bamboo for 5-7-9, and the third east wind. Throwing the 3 circles instead leaves 24, and throwing one of the east winds breaks the pair and makes the hand 3-shanten.
Count tiles that are gone. The calculator starts from four of each tile and subtracts the ones in your hand. Add discards, dora indicators and other players' called sets under Seen elsewhere and the counts drop to what can still be drawn. A wait on tiles that are all visible still counts as tenpai under the EMA rules (3.3.8), but it can never win.
How this calculator counts
Many tools use a quick formula: 8 minus twice the number of complete sets, minus partial sets, minus one for a pair. It is right for most hands but goes wrong when a hand holds all four copies of a tile. Take 1-9 of characters with four 1 circles: the formula calls it tenpai on a fifth 1 circles, which does not exist. As the EMA rulebook puts it, a hand cannot wait on a fifth copy (3.3.8). This calculator works out the fewest tiles the hand is missing from any complete hand that can really be built, never more than four of a tile, so that hand is correctly 1-shanten, and almost any draw makes it tenpai.
The tile counts can be checked against well-known shapes: the nine-sided wait 1-1-1-2-3-4-5-6-7-8-9-9-9 of one suit is tenpai on all nine tiles of its suit, 23 copies in all, and the thirteen-sided thirteen orphans wait is tenpai on 13 kinds, 39 copies.
What shanten does not tell you
- Value. Fastest is not always best. In riichi a hand needs a yaku to win, so a slower route to all simples or a dragon triplet can beat the widest one. Score the finished hand with the riichi score calculator.
- Wait quality. Ukeire counts how many tiles improve the hand, not whether the tenpai you reach waits on one tile or eight.
- Safety. When another player declares riichi, the tile that keeps your hand fastest may be the one that deals into theirs.
How likely you are to draw one of those 28 tiles in the next few turns is a card-draw probability question; Dice Parlor works out draw odds like that.