There are different types of gloves used in both baseball and softball. Infielders will use smaller gloves with shorter fingers and smaller pockets to allow them to get the ball out quicker to make a throw. Outfielders want to be able to reach balls that are further from them, and it is not as important to get the ball out quickly, so they will usually go with a larger glove. Catchers and first basemen use mitts, or larger gloves with no fingers in them, because of the nature of their position.
Baseball and softball gloves are measured from their longest finger extension point to the heel of the glove. A tape measure is run from the top of the index finger and straight down to the heel. Baseball has a 12-inch maximum at all levels. Most gloves will have a size indication imprinted somewhere on the glove.
There are some differences between baseball and softball at the youth level when it comes to the use of the catcher's mitt. The mitt for baseball is more rounded and more padded than the one in use for softball, but while most youth baseball organizations mandate the use of the catcher's mitt as early as nine or 10 years old, many youth softball catcher's opt for a regular fielder's glove, and rules do not prohibit that. Catcher's mitts for baseball and softball are similar in size, but the softball mitt has a larger pocket to handle the bigger ball. Baseball first basemen often use a mitt that is longer than a fielder's glove and has no fingers to aid in digging balls out of the dirt. There are few softball first basemen's mitts, and most softball first basemen use the longer 14-inch fielder's glove.
In both baseball and softball, the goal of the infielder is to field the ball quickly and transfer it to the glove hand. That goal leads to the determination of the size of glove infielders will wear. Baseball infielders, even in high school, college and at the professional level, prefer to use gloves in the 11-inch to a maximum 11 1/2-inch length. Some even go to a 10 3/4-inch glove. Softball players rarely use a glove smaller that 12 inches and infielders typically use one that is between 12 and 12 3/4 inches.
Most baseball outfielders use a 12-inch maximum sized glove, and some will even try to fudge the rules a little bit and use something a little longer than that, as gloves are rarely measured. Softball outfielders tend towards a 13 or 14-inch glove. As outfielders primary use for the glove is to reach as many balls as they can, the longer the glove, the better.