Measuring for a new tub

[SandyinCA]

My house is about 15 years old and I want to remove the original one piece tub/wall surround system and replace it with a separate tub and ceramic tile on the walls. When I did the measurements to see what length of tub is needed, the wall measures 58" across, but a standard tub measures 60". My question is this. Should I be measuring from stud to stud for the new bathtub or from wall to wall? My guy who is doing the tub installation says I need to get a special order 54" tub, but I'm having a hard time believing that I can't install a standard size tub in this bathroom. The current tub/surround setup fits between the 2 walls and there is no room for error or expansion. Anyone have any advise on this? This is my first bathroom remodel where I've decided to replace the tub, so I have zero experience with this.

[Cass]

Are the existing tub walls glued to the drywall or are they attatched to the studs?

[hj]

Stud to stud, and if the installer doesn't know that, then you really need a different installer.

[SandyinCA]

Cass,
I haven't removed the old unit because of this tub "issue" so I have no idea right now what it is attached to. I suspect it is attached to the drywall, as the surround piece sticks out from the wall at the point where the surround begins about a 1/2" - 3/4".
hj, thanks, I had my suspicions about that.....lol
This is an awesome forum and you have been very helpful!
Cheers!