As defined in the LL rule book:
"The STRIKE ZONE is that space over home plate which is between the batter's armpits and the top of the knees whe the batter assumes a natural stance. The umpire shall determine the strike zone according to the batter's usual stance when that batter swings at a pitch."

Home plate is 17" wide, the baseball is about 3" in diameter. So assuming only a seam of the baseball is required to be over the inner or outer part of the plate, that give us about a 23" wide strike zone. That's just shy of a 2' wide strike zone.

Each umpire works to establish his/her strike zone and each differ to various degrees. Some like low pitches, some give higher pitches, some are more liberal on the outside corner than others. What we have to do as coaches is to teach our pitchers to pitch within the umpires strike zone and teach our hitters to adjust to swinging at pitches that the umpire is calling strikes. That will change from game to game depending on who is behind the plate.

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