How Many Dominoes Are in a Set? Every Size, Counted

The box says “double-six,” “double-nine” or “double-twelve,” and that one number tells you everything else. A set named double-n holds every possible pairing of the numbers from 0 (blank) up to n, each exactly once. Count those pairings and you have the size of the set.

How many dominoes in each set size

Double-six is the “regular” set most of us grew up with. Double-twelve is the set sold for Mexican Train. Double-fifteen and double-eighteen exist for large groups; Wikipedia’s dominoes article calls double-eighteen the practical maximum.

• Double-6
• Double-9
• Double-12
• Double-15

Why a double-six set has 28 tiles

Lay the tiles out by their higher number and the count makes itself:

• Row 0: just 0-0. 1 tile.
• Row 1: 1-0, 1-1. 2 tiles.
• Row 2: 2-0, 2-1, 2-2. 3 tiles.
• …and so on, until row 6: 6-0 through 6-6. 7 tiles.

1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. Every larger set just adds rows. A double-nine set keeps going to a row of 10 (55 tiles), a double-twelve set to a row of 13 (91 tiles).

The shortcut for any set is (n + 1) × (n + 2) ÷ 2. For double-twelve: 13 × 14 ÷ 2 = 91. Mathematicians call these triangle numbers, because the rows really do make a triangle. Try it:

See every tile in a set

Double-6Double-9Double-12Double-15Double-18

Each square is one tile. Row 5, for example, holds 5-0, 5-1, 5-2, 5-3, 5-4 and the double 5-5. Darker squares on the diagonal are the doubles.

Light up every tile with a— pick a number —blank (0)123456789101112

Double-12: 91 tiles

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 = 91. That is (12 + 1) × (12 + 2) ÷ 2. 13 doubles, 1,092 spots in all.

How many tiles carry each number

Every number appears on n + 1 tiles. In a double-six set there are seven tiles with a 3 on them: 3-0, 3-1, 3-2, 3-3, 4-3, 5-3 and 6-3. In domino games these are called a “suit.” This matters when you play: if six 5s are already on the table in a double-six game, you know the last one is either in someone’s hand or in the boneyard.

Which set should you buy?

• Two to four players, classic draw or block dominoes: double-six. It is small enough that you draw and block often, which is the fun of those games.
• Mexican Train, chicken foot and other “train” games: double-twelve. Pagat.com’s rules deal 15 tiles each to up to four players, 12 each to five or six and 10 each to seven or eight. One full game is 13 rounds, one for each double. See our Mexican Train rules, or work out the deal for your table with the Mexican Train dominoes calculator.
• Nine or more at the table: double-fifteen (136 tiles). Wikipedia lists it for 9 to 12 Mexican Train players.
• A smaller, quicker Mexican Train: double-nine works for a few players and gives a game of 10 rounds instead of 13.

Comparing the two most common big sets in detail? Read double-12 vs double-15 dominoes.

Count your set in two minutes

Sets lose tiles under sofas. To check yours, sort by the higher number into rows as above. Row 0 should hold one tile, row 1 two tiles, and so on. A short row tells you which number the lost tile carries, and the tiles already in that row tell you its other end. If you would rather not count, a game of Mexican Train online always has all 91.