Asking how long a softball game is a bit like asking how long a piece of string is. It's as long as it is. Softball is different from some other sports in that it's not broken down into specific blocks of time. If the defense is good and can quickly eliminate the other team, the game will be over quickly. Otherwise, it can keep going for several hours.
A softball game is divided into innings. Each inning is broken down into two parts: the top half and the bottom half. During the top half, one team attempts to score and the other tries to prevent them from scoring. During the bottom half, the roles are reversed. Each half lasts as long as necessary for the defense to record three outs. After the innings are over, the team with the most runs wins the game.
Games typically last an hour or two, although longer and shorter games are possible. The length depends on the number of innings in the game. The typical game has seven innings, but the rules allow anywhere between three and seven innings -- or even additional innings, in the event of a tie score.
Longest Game Ever
In July 2009, two teams in Alberta, Canada set a Guinness World Record. They played softball for 115 hours and 3 minutes straight. The game started on June 30th and went on until July 5th, when the winning team walked away with a victory of 876-766.
Other Time Rules
According to International Softball Federation rules a regulation softball game is seven innings. If the teams are tied at the end of the seventh inning, they can keep going to break the tie. This can extend the game considerably. On the other hand, umpires can call the game in certain circumstances at their discretion, resulting in a shorter game.
Softball also has something called "the mercy rule." This is a rule that allows the game to end if one team has amassed a score much higher than the other team, and it seems unlikely that the losing team could catch up. This rule avoids humiliating the losing team, but it also avoids games that keep going on and on.