Riichi Mahjong · Closed 2 / open 1

Chanta (Outside Hand) in Riichi Mahjong: Han, Examples and Odds

In riichi mahjong, Chanta (honchantaiyaochuu, the "outside hand") is worth 2 han closed and 1 han open: every one of the four sets and the pair contains at least one terminal (1 or 9) or honor tile, and at least one set is a sequence.

The rules for Chanta

• Every set and the pair must include a terminal or honor: sequences can only be 1-2-3 or 7-8-9, triplets only 1s, 9s or honors
• At least one sequence; with only triplets it's honroutou instead, not chanta
• It needs honors; with no honors at all it upgrades to junchan
• Chi, pon and kan are allowed, but calling drops it one han (1 han)
• Seven pairs doesn't count (it isn't a four-sets-and-a-pair hand)

Chanta vs Junchan vs Honroutou

Only one of them ever counts: sequences plus honors is chanta, sequences without honors is junchan, no sequences at all is honroutou (plus toitoi or chiitoitsu).

How Chanta waits

Sequences can only be 1-2-3 or 7-8-9, so the waits are often edge or closed waits: 1-2 characters waits on 3, 8-9 dots on 7, 1-3 bamboo on 2. A 7-8 characters open wait takes 6 or 9, but only the 9 keeps chanta — win on the 6 and the yaku is gone.

That's why chanta is hard: most of your partial sets are edge or closed waits with few tiles that fit, and the 3s and 7s you need are tiles other players like to keep.

How Chanta is scored

The yaku, han, fu and points below are computed live by the same scoring code the game uses.

Common combinations:

How it relates to other yaku

• Junchan: also a terminal in every set, but no honors — 3 han closed. The two never stack.
• Sanshoku: a 1-2-3 or 7-8-9 sanshoku already has a terminal in every sequence, so it often comes with chanta.
• Yakuhai: an honor triplet is a terminal-or-honor set by itself. Pon a yakuhai and finish chanta, and even an open hand has 2 han or more.
• Honitsu: a chanta in one suit plus honors often gets honitsu too.
• Ittsu and tanyao can't combine with chanta (ittsu needs 4-5-6, tanyao has no terminals). Pinfu can, as long as the sequences are 1-2-3 or 7-8-9 and the pair is a suited 1 or 9.

Chanta odds

In 40,000 hands where four computers played normally on this site (33,226 wins), chanta was in 0.25% of wins, and those wins averaged 5,500 points. The speed-minded computers rarely aim for a yaku with so few useful tiles.

Source: 40,000 computer hands on this site (all four at normal level), 33,226 wins. A win usually has several yaku, so the shares add up to more than 100%.

Which hands suit Chanta

• Lots of terminals and honors in your start and few 4s, 5s and 6s — a hand that's bad for tanyao and pinfu anyway.
• A yakuhai pair: pon it and you have a yaku, so an open chanta is never yakuless.
• A possible sanshoku: a 1-2-3 or 7-8-9 sanshoku with chanta is 4 han closed.

When to give up: you still hold many 4s, 5s and 6s, or the edge and closed waits just won't fill. Going back to a normal hand is faster. To practice, open a table of free online riichi mahjong and play the computers.

Outside hands in other mahjong styles

• Sichuan mahjong's "quan dai yao": there are no honors, so every set needs a 1 or 9 — closer to junchan (Sichuan mahjong Terminals in All Sets)
• Chinese Official (Guobiao) "Outside Hand": 4 fan (Guobiao fan list)

FAQ

How many han is Chanta?

2 han closed and 1 han open (kuisagari).

Is an all-triplets chanta still chanta?

No. A hand of only terminal and honor triplets is honroutou plus toitoi. Chanta needs at least one sequence.

What about chanta with no honors?

With no honors it's junchan: 3 han closed, 2 han open. Only junchan counts.

Related yaku

Junchan Closed 3 / open 2 A 1 or 9 in every set and the pair, no honors — 3 han closed, 2 open. Junchan vs chanta, and junchan sanshoku. Honroutou Closed 2 / open 2 Only 1s, 9s and honors — 2 han even when open, always with toitoi or chiitoitsu. Examples, combos and odds. Yakuhai Closed 1 / open 1 A triplet of dragons, seat wind or round wind — 1 han, even when called. Double wind, atozuke and one-sided waits.