Tubs that fit in alcoves are 60" long.
Most rooms are framed in at 60-1/4"
Drywall will take up about 1-1/4"
Tile will take up more space, so that mostly you will find 58" between the walls when finished plus or minus.
We're going to remodel our condo master bath. The current tub is a plastic type and I want to put in cast iron. When I measure the what appears to be the length of the the tub - it looked like 57". All the cast iron ones at Depot are 60". Do standard tub sizes vary like this or is it a one size fits all type of thing and I'm not accounting for the sheet rock?
I believe the mesaurement is from sheetrock edge to sheetrock edge just forward of the tub opening.