The English used in this article may not be easy for everybody to understand. (July 2012)
The strike zone is the area over home plate through which a pitch must pass to be called a strike, roughly between the batter's armpits and knees. The Strike Zone shall be determined from the batter's stance as the batter is prepared to swing at a pitched ball. The strike zone in baseball is a tricky subject as the strike zone changes with each batter. Accordingly, there is no "automatic" strike zone and much of what is a strike or not a strike is left to the judgement of the home plate umpire.
In short, the strike zone extends from the batters' knees to the letters across the front of his uniform. To be called a strike, the pitcher must throw the baseball across home plate, an area 17 inches wide (0.4318 meters), and between the knees and letters as indicated. In professional baseball, a player who stands 5' 6" tall (1.67 meters), for example, will have a much smaller strike zone that will a 6' 4" (1.93 meters) homerun hitter. Moreover, the focus is not on where the ball is caught by the catcher, but rather where the ball is as it passes the front of home plate.