The most common shower doors are 60 inches wide for standard bathtub showers and 48 inches to 60 inches wide for standalone shower stalls. Both of these are bypass type doors, a style that encompasses a pair of doors that slide past each other on a track.
Smaller showers have doors less than 48 inches wide, but are generally pivot style doors rather than the traditional bypass type. Finding the right door for an existing shower involves measuring both the opening width and height. Width should be measured from wall to wall, at both the top and bottom of the opening. Height is measured from the top of the wall to the top of the shower base or tub edge.