What Are the Rough In Dimensions For a Shower Door?

Luxury Bathroom with Tile Floor
Luxury Bathroom with Tile Floor. Getty / Vladimir Godnik

Question: Rough In Dimensions For Shower Door

I'm in the middle or a master bathroom renovation. I'm replacing the old shower fiberglass surround with tile. I'm confident with the tile and waterproofing part but I'm having a tough time finding a solid answer to the simple question of how wide to make the shower opening for a specific door width.

The shower area is 36" across. I'd like to install a 30" frameless glass door. Outside the shower, the wall juts out and will only allow clearance for a 30" door. (the previous door was larger but I brought out the depth of the shower by 6").

So I have to bring in the shower opening to accommodate the door and I can't find a good rule-of-thumb for the space needed from stud-to-stud for the door area and I'm fearful I'll make the space too narrow.

The tile to be used in the shower will be a natural stone 3/8" thick. But with tile, cement board, thinset, hinges, etc. to consider I'd like to make sure I get this right.

I've Googled every possible search criteria I can imagine, but of course, ​I'm only finding solutions to measuring an existing opening to determine what size door to use, never the other way around.

Answer: I understand your dilemma, especially since it's pretty irreversible (or extremely difficult to reverse) once you construct that door opening.

As you probably know, frameless shower doors tend to have one or even two glass side pieces (side lights). The hinge-side piece allows the door to pivot open and closed while maintaining a waterproof seal against the shower wall.

I'm having a hard time picturing the part that juts out. What's certain is that you say nothing more than a 30" door can be used, because of the swing. So for instance, if you have a 33" door, it would only open 45 degrees or less, whereas a 30" door would open the entire 90 degrees or even more?

If you plan on a side light, it might give the door enough room so that it can open 45 degrees.

But that aside, all but one of the dimensions--tile, cement board, and shower door unit--are fixed. Some shower door retailers have detailed spec information on their sites which tell you the rough opening needed.

Both cement board and stone should be specified as true dimensions (e.g., 3/8" thick should mean 3/8" thick). Hinges (and brackets, strike jambs, and all other shower hardware) you can take out of the equation, since they will be included in the door opening technical information.

The only unfixed, malleable dimension is the thickness of the thinset, but it's far less than you might expect. While it looks like a lot when troweled on, it only comes out to 1/16" to 1/8" after the tile is pressed into place.

But in the end, how many frameless shower door units do you have to choose from with an absolute maximum available opening of 36"? I'm guessing about two (which is a good, because it narrows things down for you). There would be one of about 30" and another of about 33". After that, the dimensions likely hit 36" and upward from there.