How wide is a strike zone?

Answer 1

In MLB, this is covered in Rule 2.0: "The Strike Zone is defined as that area over homeplate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the hollow beneath the kneecap. The Strike Zone shall be determined from the batter's stance as the batter is prepared to swing at a pitched ball." Home plate is 17 inches wide.

Answer 2

The With of the plate and from the hitters knees to his chest