Domino sets come in several standard sizes, each with a different number of dominoes. The double-six set is one of the most popular, and it works well for playing most games. However, you may want to use a larger set if you have lots of players, if you're playing a complex game or if you want the game to last longer.
The three most common types of domino sets are the double-six, the double-nine and the double-12. The double-six set has 28 dominoes, with the lowest (also called the lightest) being the double blank and the highest (or heaviest) being the double six. Double-nine sets have 55 dominoes, ending with the double nine, and double-12 sets have 91 dominoes. Less common sets may include the double-15, with 136 dominoes, and the double-18with 190.
How many dominoes you need depends on the game you want to play and the number of players. A double-six set will allow two to four players to play most domino games. For four to six players, you may want to use a double-nine set. A double-12 set can support up to ten players. Larger sets can work especially well for games such as Mexican Train, Chickenfoot and Tiddle-a-Wink, and double-12 sets also work well for playing solitaire games such as Castle Rock and Concentration. If you use a large set for only a few players, you may need to adjust the number of dominoes with which each player starts.
For many games, the number of dominoes you choose to play with can affect the length of the game. A basic game of draw dominoes will take significantly longer for two players if you use a double-12 set than if you use a double-six. If each player draws seven dominoes, there will be 14 dominoes left to draw with a double-six set, but 77 dominoes in the draw pile with a double-12 set. In games with a set number of rounds, such as Moon, or that don't allow players to draw additional tiles, such as block dominoes, the number of dominoes may not increase the length of the game.
For most games, if you use a large domino set, or many players, you'll need a lot more table space to arrange the dominoes than you would with a basic double-six set. In general, block and point style domino games, which require players to arrange the dominoes on a flat surface, matching them end to end, take up more room than card style domino games, such as Texas 42. If you have limited space, you may want to play with the smallest set that seems reasonable for a particular game.
Most domino sets use dots to indicate the value of each tile, but some use printed numbers, like cards. This can be especially useful for large sets, such as the double-15 and double-18 when the number of dots can be difficult to count. Some domino sets also use different colors for each set of dots, making it easier to tell them apart, especially for young children.