It must be exactly 60 inches.
How wide is an average shower door.
Bypass or sliding door dimensions alcove shower bathtubs commonly are 60 inches wide and their bypass or sliding doors are usually about 58 inches.
If the width is longer than 36 inches you may have to include an extra panel to the door to support the weight of the structure.
When framing the alcove do not add any extra space to accommodate the shower tub.
Measure the opening height.
This dimension might be direct to stud or between two wall coverings.
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The total height of an enclosure is determined from off the top of the curb threshold or step over where the door will be located going up.
If trying to do a single fixed panel glass shower screen try to use a rain shower head and for the hand sprayer spray away from the opening toward the front of the shower and you will be fine.
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In general the width of a shower door should be between 22 inches and 36 inches.
Determine the distance from the top of the tub edge or shower base to the top of the wall unit or tile wall where you want the door to be located.
If these differ select a door using the larger width for a bypass door or the smaller width for a pivot door.
With a 48 opening you may want to go with a 32 door as a 24 panel probably won t contain the water even with a rain shower to your liking.