Poured concrete foundation walls that are less than 8 feet tall and have soil outside that is 6 or 7 feet deep against the wall can often be 8 inches thick and function quite well.
Poured concrete retaining wall height.
In general the top of the stem of any cast concrete retaining wall should not be less than 12 inches for the proper placement of concrete.
They are generally economical up to 10 feet in height for cast concrete structures.
For example if you are pouring a retaining wall that will be 12 inches thick and will use wooden planks that are 1 1 2 inches thick for your forms you ll need to space the stakes about 15 inches apart 12 inches for the retaining wall plus two pieces of 1 1 2 inch thick wooden board.
Concrete retaining wall footing size the depth to the bottom of the base slab should be kept at a minimum of two feet.
Recommendations there are some basic rules of thumb for foundation wall thickness and these are outlined in many modern building codes.