What is Toitsu? Meaning, Usage, and Relationship with Jantou Explained for Beginners

What is Toitsu (Pair)?

Toitsu (対子) is a pair of 2 identical tiles in mahjong. For example, 3-man 3-man (33m) or White-White are toitsu.

Toitsu is a basic element of hand composition that can become the jantou (pair in winning hand) or develop into a koutsu (triplet). It’s an important shape in hand building.

Detailed Explanation of Toitsu

Roles of Toitsu

Role	Explanation	Example
Becomes Jantou	Required pair for winning	Need exactly 1 for win
Develops to Koutsu	1 more tile makes triplet	Complete via pon or tsumo
Chiitoitsu Component	7 pairs to win	Special yaku

Types of Toitsu

Numbered Tile Pairs
- Man: 11m, 55m, 99m, etc.
- Pin: 22p, 66p, 88p, etc.
- Sou: 33s, 77s, 99s, etc.
Honor Tile Pairs
- Winds: East-East, South-South, West-West, North-North
- Dragons: White-White, Green-Green, Red-Red

Number of Pairs and Hand Building

Pair Count	Direction	Notes
0	Sequence-focused	Watch for missing jantou
1	Balanced	Ideal
2	Room for choice	Decide which becomes jantou
3+	Pair overflow	Consider chiitoitsu or toitoi

Usage Examples

Real Game Situations

Example 1: Hand Structure

"Only have 1 pair, this will be my jantou"
"4 pairs...maybe go for chiitoitsu"

Example 2: Pon Decision

"Have a yakuhai pair, let's pon for guaranteed 1 han"
"Have a dora pair, really want to pon this"

Example 3: Pair Management

"Too many pairs, let's break one into taatsu"
"Keep the safe tile pair until the end"

Relationship Between Toitsu and Jantou

What is Jantou?

Definition: The pair in a completed winning hand
Required: Need exactly 1 for standard win
Also called: Atama (head), Gan (eye)

From Toitsu to Jantou

Pair in hand → On winning → Jantou
    55m        Complete      Head

Jantou: Pair in winning hand
Koutsu: 3 identical tiles
Chiitoitsu: Yaku with 7 pairs
Toitoi: All triplets yaku
Shanpon Machi: Wait on 2 pairs

Common Mistakes and Points to Note

Points Beginners Often Mistake

Too Many Pairs
- 3+ is concerning
- Hand won’t progress toward sets
Forgetting Jantou
- Have 4 sets but no pair
- May end up in tanki wait
Carelessly Discarding Pairs
- Discarding yakuhai pairs
- Often regret later
Miscounting Pairs
- Counting ankous as pairs
- Strictly 2-tile pairs only

Hand Building with Pairs

When You Have Few Pairs (0-1)

Sequence-focused building
Aim for pinfu
Prioritize ryanmen waits

When You Have Many Pairs (3+)

Chiitoitsu Route
- Consider at 4+ pairs
- Also good for defense
Toitoi Route
- Build triplets
- Progress by calling
Break Pairs
- Consecutive numbers can become taatsu
- Restore balance

Yaku Where Pairs Matter

Yaku Name	How Pairs Are Used
Chiitoitsu	Made of 7 pairs
Ryanpeikou	Same sequence twice (pairs × 3)
Toitoi	All triplets (developed from pairs)

Strategic Points

Evaluating Pair Value

Yakuhai Pairs
- Highest value
- Guaranteed 1 han
Dora Pairs
- Direct score increase
- Use actively
Terminal/Honor Pairs
- Useful as safe tiles
- Good jantou candidates
Simple Tile Pairs
- Can also develop to sequences
- Flexible

Conclusion

Toitsu is a simple shape of 2 identical tiles but plays very important roles in mahjong. It’s essential as jantou, can develop into koutsu, and is even the building block of the special yaku chiitoitsu. Beginners should always be aware of pair count and maintain balance—not too many, not too few. Master pair management and you’ll be able to build hands flexibly.