A standard double-six set of dominoes contains 28 tiles with a total of 168 spots. Another commonly used set of dominoes is the double-nine, which contains 55 tiles with a total of 495 spots.
While double-six and double-nine are the most commonly used sets of dominoes, larger sets are available for players who want very long games or who plan to play in large groups.
It is possible to determine the number of spots in a domino set of any size by using the formula (n+1)(n+2) / 2, where n equals the largest value available in the set. The spots on a domino set are also sometimes known as dots or pips.