I'm interested in installing a prefab tub suround to replace the tile. But am not sure how to measure for the correct size. Do I measure from the finished walls above the tub, the finished alcove size, or do I use the actual tub dimensions?
the surround will come in standard sizes with some flexibility. You measure the rough opening. So measure from the back wall to the tub edge add 1/2" for the drywall and 1/2" for the tile and thinset. Double this (add 2") for the length.