Double-six, -nine or -twelve: which domino set should you own?

Buy the set your game calls for. If you play line games — block, draw, All Fives, Fives and Threes, or the partnership games of the Caribbean and Latin America — that is a double-six set of 28 tiles. If you play Cuban-style partnership, or Chicken Foot, you want a double-nine of 55. If you play Mexican Train, you want a double-twelve of 91. Double-fifteen and double-eighteen sets exist for big groups playing train and foot games. Because each larger set contains every smaller one, a bigger set can also play the smaller games — but you have to sort tiles out first.

What is in each set

A set named "double-n" holds one tile for every pair of numbers from 0 (blank) to n, so the count grows quickly. These are exact:

Set	Tiles	Doubles	Tiles carrying any one number	Total pips	Average pips per tile
Double-six	28	7	7	168	6
Double-nine	55	10	10	495	9
Double-twelve	91	13	13	1,092	12
Double-fifteen	136	16	16	2,040	15
Double-eighteen	190	19	19	3,420	18

The tile count is (n+1)(n+2)/2. Each number appears on n+1 tiles: the double, plus one tile pairing it with every other number. Wikipedia calls double-eighteen the largest set in practical use. Pagat.com, the standard rules reference for card and tile games, says the double-nine has existed since at least the early 20th century, and that larger sets became popular more recently for some North American games, Mexican Train above all.

Why a bigger set is a different game

Three things change as the set grows, and each changes how you play.

Matching gets harder. In a double-six set, a quarter of all tiles (7 of 28) carry any given number. In a double-nine it is 10 of 55, about 18%. In a double-twelve it is 13 of 91, about 14%. In a double-eighteen it is one tile in ten. That is why games for big sets give everyone a lot of tiles and a boneyard to draw from: with only seven tiles from a double-twelve, you would be stuck almost every turn.

Hands get heavier. The average tile in a double-n set carries n pips, so the average hand is simply tiles held × n. A seven-tile double-six hand averages 42 pips. A ten-tile hand from a double-nine averages 90. A fifteen-tile Mexican Train hand from a double-twelve averages 180. If your table scores by the pips left in losers' hands, the numbers you play to — and how bad it is to be caught holding tiles — scale with the set. (See how a domino game is scored for the systems.)

Counting gets harder, and luck rises. With a double-six you track seven tiles per number. With a double-nine you track ten, and in most double-nine games some tiles are never dealt at all. That is the bigger change.

Sleeping tiles: the hidden difference

In partnership double-six — the Jamaican partner game and the Mexican, Colombian and Venezuelan games pagat.com describes — four players take seven tiles each and all 28 are in play. Every tile you cannot see is in someone's hand, and every pass tells you something certain.

Cuban partnership, as pagat describes it, uses a double-nine. Four players take ten tiles each, and the other 15 lie face down for the whole round. From your seat, 45 tiles are unseen, but only 30 of them are in other hands. Any tile you have not seen has a one-in-three chance of being asleep. A pass still narrows things, but not to certainty, and the count of what remains is always a guess about the sleeping tiles.

This changes the endgame too. With all 28 double-six tiles dealt, a blocked game can only happen with the same number at both ends, and with all seven of that number already played (the parity rule). With sleeping tiles, that guarantee goes: a game can block with different numbers showing, because the tiles that would have opened it are face down.

The size of each hand also changes how often you are stuck from the start. A seven-tile double-six hand has a 9.8% chance of holding no tile at all of a given number. A ten-tile double-nine hand has 10.9%. A fifteen-tile double-twelve hand has 8.0%. These are exact figures. They are close because the games deal hand sizes that suit each set — which is the reason those deal sizes exist.

Pagat also notes that the Cuban partnership game is sometimes played with a double-six set, seven tiles each, all in play. If your table plays Cuban rules on a double-six, the arithmetic above is the double-six arithmetic.

What each set is for

Double-six (28 tiles). Two to four players. It suits every classic line game: block, draw, All Fives, Fives and Threes (Britain's pub and league game, per Wikipedia), and the partnership game played across the Caribbean and Latin America. Hands are short and the whole set can be counted in your head. If you are buying one set and you do not play train games, buy this one.

Double-nine (55 tiles). Pagat lists it for Cuban partnership (ten each, 15 asleep, to 100 points), Longana, and Chicken Foot. For Chicken Foot, pagat reproduces a deal table from the manufacturer Puremco: 20 tiles each for two players, 14 for three, 11 for four, 9 for five and 7 for six, with smaller deals also suggested. A Chicken Foot game with a double-nine is ten hands, one for each starting double from 9-9 down to 0-0, and the double-blank caught in hand counts 50 points.

Double-twelve (91 tiles). The Mexican Train set. Pagat deals 15 tiles each for up to four players, 12 for five or six, 10 for seven or eight, and 8 for nine or ten. A full session is 13 games, starting from 12-12 and working down to 0-0, and the lowest total wins. Other published rule sheets use different deal counts; agree yours before the first hand. Even with eight players taking ten each, 11 tiles stay in the boneyard; with four players, 31 do.

Double-fifteen (136) and double-eighteen (190). For large groups. In the same Puremco table, a double-fifteen handles six to twelve Chicken Foot players and a double-eighteen seven to fifteen. Unless you regularly host a crowd, you do not need one.

One set or several?

Every double-nine set contains a complete double-six: take out the 27 tiles that carry a 7, 8 or 9, and the 28 left are the double-six set. A double-twelve contains a full double-nine (remove 36 tiles) and a full double-six (remove 63). So one large set can serve several games.

The catch is the sorting. Pulling 27 tiles out before every partnership session is tedious, and one stray [6-8] in a double-six game breaks every count at the table. If you play both kinds of game often, two sets are easier than one.

Pips, numerals and colours

Counting nine dots at a glance is slower than counting six, and twelve is slower still. Wikipedia notes that modern sets commonly give each number its own dot colour, and that large sets often print numerals instead of pips for readability. For train and foot games with double-twelve or bigger, colour-coded pips or numerals make the game faster. For double-six games, plain pips are traditional, and most players read them instantly.

Material is a matter of taste. Wikipedia lists the traditional European materials as bone, ivory, mother of pearl and dark hardwoods such as ebony; modern commercial sets are mostly ABS or polystyrene plastics, sometimes Bakelite or other phenolic resins.

A note on Chinese dominoes

A Chinese domino set is a different thing. Pagat describes it as 32 tiles with ends from 1 to 6 and no blanks, matching the throws of two dice, with some tiles duplicated. It is used for its own family of games. It will not play any of the games above.

The short version

You play	Buy
Block, draw, All Fives, Fives and Threes	Double-six
Caribbean or Latin American partnership	Double-six
Cuban partnership (most tables)	Double-nine
Chicken Foot, up to six players	Double-nine
Mexican Train	Double-twelve
Chicken Foot or trains for ten or more	Double-fifteen or double-eighteen

For how these games differ beyond the set, see the main domino games and how they differ.