Marbles have been around for ages and, for most of that time, they have come in sizes ranging from as tiny as a pea to as big as a small ball. Marble size is a matter of preference for hobbyists, but, as of 2011, the National Marbles Tournament called for specific sized marbles for its competitions.
Small
The three smallest sizes of marbles are 12 mm in diameter, 9/16 of an inch diameter and 5/8 of an inch diameter. The 12 mm marbles are slightly smaller than a Chinese checker marble and are not used in standard games. The 9/16 of an inch marble is used most often for Chinese checkers. The 5/8 of an inch size is the kind most used in marble games and as decoration.
Medium
Competitive marble players tend to have few medium-sized marbles. The 3/4 of an inch marble, for example, is known as a "shooter." Each player needs only two or three shooters for competitions. The 7/8 of an inch marble is an unusual size and not allowed in standard game play. Outside the North America, 1-inch marbles are sometimes used as shooters.
Large
Large marbles are uncommon in game play unless players have made modifications to the rules. Marbles over an inch in size are called boulders, and not are not allowed in standard games. In marble sets and marble runs, the 1 3/8 of an inch and the 1 5/8 of an inch marbles are the more common choices.
Extra Large
Extra large marbles, or marbles larger than 2 inches are rarely used in official games. They are usually used by artists specializing in marble art. The extra size lends itself to elaborate designs, and the clear large marbles can even hold small objects. These kinds of marbles could sell for more than $100 as of 2011. Since the point of them is artistic expression, these marbles are not intended for any kind of play.