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.
This is shown as the distance from the finished wall surface to the center of the riser pipe the pipe that goes from the shower valve up to the shower head.
The valve height depends on if it is a tub and shower combo or just a shower.
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.
A stand alone shower you can raise it up to about 42 inches from the floor.
Employ your helper to hold the fixture at an estimated height and then see if it s a comfortable reach for all users.
For shower only controls between 36 and 48 inches from the floor is common.
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.
A height of 28 inches or 2 feet 4 inches is standard for valves in bathtub shower units.
Look at the shower valve installation instruction sheet for the depth distance.
Showers set in bathtubs require lower valve heights because the valve must connect to both the shower and the bath tap.