For a tub you would want it low enough to reach without standing up but still high enough to reach without bending over when taking a shower.
Shower valve distance from floor.
For shower only controls between 36 and 48 inches from the floor is common.
A stand alone shower you can raise it up to about 42 inches from the floor.
Subtract the thickness of your finished wall from the depth distance to find the pipe depth.
About 33 inches from the floor.
Showers set in bathtubs require lower valve heights because the valve must connect to both the shower and the bath tap.
The height of the valve for a shower depends upon whether you need it for a shower stall or a shower set in a bathtub.
Shower controls should be placed at a height 40 50 102 127 cm above the shower floor and out of direct line of the water path to avoid being caught in extremely cold or hot water when operating.
The lower crosspiece which will hold the shower valve may be around 50 inches from the floor for a shower enclosure and lower for a bathtub just enough to clear the lip of the tub by a few.
Shower heads are located at a standard height of 80 203 cm but can be set at a minimum height of 72 183 cm if desired.
The valve height depends on if it is a tub and shower combo or just a shower.
Employ your helper to hold the fixture at an estimated height and then see if it s a comfortable reach for all users.