Winning Hand Structure

4.1 The Standard Winning Pattern: 4 Mentsu + 1 Jantai

The vast majority of winning hands in riichi mahjong follow the standard pattern: four groups (面子, mentsu) plus one pair (雀頭, jantai). Since a complete hand consists of 14 tiles (13 in hand plus the winning tile), this pattern accounts for: 4 groups × 3 tiles each = 12 tiles, plus 1 pair × 2 tiles = 14 tiles total.

A group (mentsu) can be either:

Sequence (順子, shuntsu): Three consecutively numbered tiles of the same suit. For example, 2m-3m-4m or 5p-6p-7p. Sequences can only be formed from suited tiles (manzu, pinzu, souzu)—honor tiles cannot form sequences. The sequence must be exactly three consecutive numbers; you cannot "wrap around" from 9 to 1.

Triplet (刻子, koutsu): Three identical tiles. For example, 7s-7s-7s or East-East-East. Any tile type can form a triplet, including honor tiles. Triplets can be closed (concealed in hand, 暗刻 ankou) or open (formed by calling pon, 明刻 minkou).

The pair (jantai/雀頭) is two identical tiles. Every standard winning hand must have exactly one pair. The choice of pair matters for scoring (certain pairs contribute fu) and for yaku (some yaku restrict which tiles can be the pair).

4.2 Quad Groups (槓子, Kantsu)

A kan (槓) is a group of four identical tiles. For the purposes of hand structure, a kan counts as one mentsu (group), just like a triplet or sequence. A hand with one kan still has 4 mentsu + 1 pair, but the total tile count is 15 (one extra tile drawn as replacement from the dead wall). Kans are covered in detail in Module 26.

4.3 Special Winning Patterns

Two special hand patterns deviate from the standard 4+1 structure:

Chiitoitsu (七対子) — Seven Pairs

A hand consisting of exactly seven distinct pairs. No mentsu groups at all—just seven pairs. Each pair must be of a different tile; you cannot use four of the same tile as two pairs. Chiitoitsu is worth 2 han (closed only) and is always counted as 25 fu by convention. This hand is relatively uncommon but provides an alternative hand-building path, especially when your starting hand has many isolated pairs.

Kokushi Musou (国士無双) — Thirteen Orphans

A hand containing one each of all 13 yaochuuhai (terminals and honors): 1m, 9m, 1p, 9p, 1s, 9s, 1z, 2z, 3z, 4z, 5z, 6z, 7z—plus one duplicate of any of these 13 tiles to form the pair. This is a yakuman (limit hand worth the maximum score). Kokushi completely ignores the normal mentsu structure. It requires collecting exactly these 13 specific tile types, making it a rare but spectacular hand.

4.4 The Yaku Requirement

Completing the correct tile pattern is necessary but not sufficient to win. You must also have at least one yaku (役)—a scoring pattern or condition that validates your hand. A hand with a valid tile structure but zero yaku cannot be declared as a win. This is one of the most common sources of confusion for beginners transitioning from other mahjong variants. The yaku system is covered comprehensively in Module 10.

4.5 Agari: Tsumo and Ron

There are two ways to complete your winning hand:

Tsumo (自摸/ツモ): You draw the winning tile yourself from the wall. When you win by tsumo, all three opponents pay you. The payment split depends on whether you are the dealer (all three pay equal shares) or a non-dealer (the dealer pays more, the other two pay less).

Ron (ロン/栄): Another player discards the tile you need. When you win by ron, only the player who discarded the winning tile pays you the full amount. However, ron is subject to the furiten rule (Module 6)—if any of your winning tiles exists in your own discard pool, you cannot win by ron.

4.6 How to Identify Valid Groupings

When you have 14 tiles, you must determine whether they can be arranged into 4 mentsu + 1 pair (or one of the special patterns). Sometimes a set of tiles can be grouped in multiple valid ways, each resulting in different wait types and potentially different yaku or fu. Choosing the optimal grouping matters for scoring.

4.7 Common Beginner Mistakes

Mistake: Forgetting the yaku requirement. New players often assemble a complete tile pattern and attempt to declare a win, only to discover they have no valid yaku. This is especially common with open hands where tanyao is the only possible yaku but the hand contains a terminal or honor tile.

Mistake: Treating four of a tile as two pairs for standard hands. In the standard 4+1 pattern, you can only have one pair. Four identical tiles must be either a kan (declared) or used as a triplet + one tile in another group. Only in chiitoitsu can you have multiple pairs—but even then, four of a kind cannot be split into two pairs of the same tile.

Mistake: Attempting to form honor sequences. East-South-West is not a valid sequence. Honor tiles can only form triplets or kans.

4.8 Recognizing Complete Hands Quickly — Pattern Training

The ability to instantly recognize whether 14 tiles form a valid winning hand is a skill that develops with practice. In competitive play and on online platforms where time limits exist, you cannot spend 30 seconds analyzing your hand structure on every draw. The standard Japanese training approach, described in Fukuchi Makoto's (福地誠) 『麻雀 定石「何切る」301選』(Maajan Jouseki "Nani Kiru" 301-sen, "Mahjong Standard Plays: 301 What-to-Cut Problems"), is to practice with dealing hands from a physical set and sorting them as quickly as possible, identifying all complete mentsu, partial groups, and the pair.

A useful beginner exercise: deal yourself 14 random tiles and time how long it takes to determine if the hand is a valid winning hand (and if not, what your shanten count is). With practice, this time should decrease from 30+ seconds to under 5 seconds. Online platforms like Tenhou handle win validation automatically, but understanding hand structure is still essential for making correct discard decisions.

4.9 Multiple Interpretations of the Same 14 Tiles

A crucial advanced concept: the same 14 tiles can sometimes be grouped in more than one valid way, and the choice of grouping affects the wait type, fu count, and even which yaku apply. This concept is called "面子の取り方" (mentsu no torikata, "meld interpretation") and is discussed in detail in井出洋介 (Ide Yousuke)'s instructional works.